International Journal of Epidemiology © Oxford University Press 1979
Vol. 8 No. 1 Printed in Great Britain
The Epidemiology of Entamoeba Histolytica in a Nigerian Urban Population J P O OYERINDE 1 , A A ALONGE, A F ADEGBITE-HOLLIST and O OGUNBI
spread of the parasite. Those who did not reply to any of the questions or whose specimens could not be examined for any reason are not Included in the results.
INTRODUCTION
In Nigeria Entamoeba bistolytica is known to exist in people of both sexes and all age-groups. Transmission of the parasite is closely associated with environmental sanitation, hygiene and personal habits. In a recent communication (1) a prevalence of 9.5% was reported for a segment of the population. This report describes the prevalence of Entamoeba histolytica and possible modes of infection among the various categories of people in the population.
RESULTS Microscopic examination of one to three faeces samples from 2 797 persons revealed infection with Entamoeba bistolytica in 312 (11.2%) - 123 (10.6%) of males and 189 (11.5%) of females. Table 1 gives the age—sex specific prevalence and shows that the infection was more common in older agegroups. Lagos is a cosmopolitan city where every ethnic group in the country is represented. The prevalence in different ethnic groups was very variable ranging from 0.0% among the Itshekiris and the Ijaws to some 25% or more among the Efik, Benin and Urhobo (Table 2). Although the numbers examined in some groups, eg Urhobos, Hausa/Fulani etc were small the proportions represent the composition of the population. To examine whether or not infection was acquired before arriving in Lagos, information was obtained from respondents on their date of arrival. The highest infection rate, 18.4% was in those who had lived in the city continuously for more than 8 years those who had lived in the city for 3, 2 and 1 years had rates of 13.9%, 8.2% and 5.2% respectively.
MATERIALS AND METHODS A total of 2 825 persons consisting of 1 163 males and 1 662 females from 10 sample survey areas of the Metropolitan Lagos, as mapped out by Morgan and Kannistro (2), participated in the study. From one to three stool samples were collected from each person and unformed stools were examined for active trophozoites, as quickly as possible. The rest were then concentrated by the formol-saline-ether technique and examined after staining in iodine. Information was obtained from every subject on his or her eating habit, type of toilet facility, water supply and other factors likely to be concerned in Department of Microbiology and Parasitology, College of Medicine, University of Lagos, PMB 12003, Lagos, Nigeria.
55
Downloaded from http://ije.oxfordjournals.org/ at Monash University on June 20, 2015
Oyerinde JPO (Department of Microbiology and Parasitology, College of Medicine, University of Lagos, PMB 12003, Lagos, Nigeria), Alonge A A, Adegbite-Hollist A F and Ogunbi 0 . The epidemiology of Entamoeba histolytica in a Nigerian urban population. International Journal of Epidemiology 1979, 8: 55—59. Microscopic examination of multiple faeces samples of 2 825 persons was carried out in the Metropolitan Lagos. Overall prevalence of Entamoeba histolytica was 11.2%. Prevalence increased rapidly in younger age groups and there were no real differences between males and females. Prevalence was high among families who ate together from the same plate, among those who ate with their fingers and among those who ate away from home. Prevalence was not associated with type of water supply but was seemingly influenced by storage of household supplies. A low infection rate was associated with the availability of water closets and toilet habit. No association was found between prevalence and standard of education but the rate of infection was increased among workers with high occupational interaction. Significant differences were found among different ethnic groups. The highest infection rate was recorded in the last month of the wet season.
56
INTERNATIONAL JOURNAL OF EPIDEMIOLOGY TABLE 1
Prevalence of Entamoeba bistolytica infection by age-group and sex Males
Age in years Under Vi Vi-\
1-5
6-15 16-25 26-35 36-45 46-55 56+
Tot*!
No Examined*
Total
Females No Examined*
% Positive
% Positive
No Examined*
% Positive
35 42 320 380 132 90 97 37 23
0.0 2.4 6.3 11.1 14.3 16.6 16.4 18.9 13.0
43 57 314 366 287 220 145 58 51
0.0 1.9 5.7 11.8 13.9 17.7 11.7 12.0 23.5
78 99 634 846 419 310 242 95 74
0.0 2.0 6.0 11.5 14.0 17.4 13.6 14.7 20.2
1156
10.6
1641
11.5
2797
11.2
TABLE 2
Prevalence of Entamoeba bistolytica by ethnic groupings and sex No Examined*
Yoruba Hausa/Fulani Ibo Benin Itshckiri Urhobo Efik Ijaw Other Nigerian
2534 15 92 15 35 6 33 47 21
infection
Positive 11.2 13.3 16.3 26.7 0.0 33.3 24.2 0.0 4.8
number excludes those who did not respond to this question and/or whose results could not be recorded for various reasons TABLE 3
Influence of education on prevalence of Entamoeba bistolytica infection —No Examined*
University Teacher Training Trade or commercial Vocational/professional Secondary Modern Primary Private No formal education
4 5 9 19 264 47 964 37 1158
%
Positive 25.0 40.0 0.0 5.2 17.0 21.2 13.0 5.4 10.0
number excludes those who did not respond to this question and/or whose remits could not be recorded for various reasons
No association was found between size of family and infection: prevalence varied between 7.8% among families with 8 members to 17.8% in the families consisting of only 2 persons. No association was found between standard of education and infection (Table 3). These findings must be interpreted cautiously however in view of the method of sampling and the small numbers of highly educated respondents. Prevalence varied significantly in different occupational groups. A high infection rate was associated with occupations where interaction among the workers was high, semi-skilled 17.9%, unskilled 16.5%, and residual categories 15.1%. The lowest prevalence occurred when occupational interaction was minimal as in the senior category with an infection rate of 7.4%, or where occupational interaction was nil as in the unemployed group (6.7%) and housewives (10.5%). Two types of climate predominate in the country, a wet season between mid-April and mid-October, and a dry season. During the wet season 2 020 people were examined and 218 (10.7%) were infected: in the dry season 576 people were examined and 110 (19.1%) were infected. The monthly rate of infection is shown in Figure 1. The majority of the respondents drank tap water: others drank well or spring water. The infection rate was 12.4% among those who had tap-water in their homes, 10.9% among those who obtained their drinking water from carriers and 10.6% among those who relied on local pump water. The highest rate (23.4%) was in those who drank well water but none of those who relied on spring water were infected. The prevalence in those who
Downloaded from http://ije.oxfordjournals.org/ at Monash University on June 20, 2015
* number excludes those who did not respond to this question and/or whose results could not be recorded for various reasons.
ENTAMOEBA HISTOLYTICA INFECTION IN NIGERIA 30
-
Ihy WET
Jw»
My
Aug.
Stpt
Oct
Nov.
SEASON
Dec.
Jin.
DRY MONTHS
OF
THE
Ftb.
Mn
SEASON
YEAR
Monthly fluctuations in the prevalence of E. bistolytica infections with the prevailing climatic conditions
cleaned their water containers daily was 9.2% and this increased significantly to 12.8% among those who stored their drinking water for 2 days. Following this, prevalence declined with increasing length of storage to 7.1% at 7 days. 15.0% of those who prepared food either for their families or for the public as a profession were infected with Entamoeba bistolytica. The highest infection rate of 39% (16/41) was in those selling uncooked food; one person out of seven examined (14.2%) from among those engaged in food manufacture was infected. The prevalence of infection was 11.8% for those selling cooked food, 8.5% for those involved in food preparation and
4.9% for those whose duty was merely to serve food. A prevalence of 12.3% was found in families whose members ate together from the same plate and 10.5% for those who ate separately. 11.9% of those who ate with their fingers were infected, compared with only 6.8% of those using cutlery. A prevalence of 12.1% was also found among those who ate elsewhere than in their homes as compared to 6.5% for those who only ate at home. An attempt to correlate prevalence with the type of food eaten, that is, whether cooked or uncooked, whether hot, cold or raw, failed as the data were too complex to analyse, mainly because of the diversity within individual diets.
Downloaded from http://ije.oxfordjournals.org/ at Monash University on June 20, 2015
Apr.
FIGURE 1
57
58
INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
An infection rate of 10.7% was associated with the availability of a water closet, while rates among those who deposited faeces in buckets and in pits were 12.1% and 13.4% respectively. Those who gave no specific means of faeces disposal had an infection rate of 9.5%, such people depending either on a neighbour's or the public facilities. 14.6% of those who used water for cleaning after passing faeces were infected, compared with 9.9% of those using toilet papers.
The high prevalence of infection (23.4%) found among those who drank well water could possibly have resulted from the fact that in homes of such people, the pit latrine is the most common means of faeces disposal. The well is usually situated close to the latrine and seepage might occur. Another source of infection might be through the containers used to draw the water. It is also known that coliform bacteria are frequently isolated from bacteriological examination of tap-water which suggests some degree of faecal contamination. This might explain the high prevalence of 12.4% in those who drank tap water. The rate of infection with Entamoeba bistolytica did not differ according to whether respondents used tap water, water brought from carriers or water from the local pump. Investigations into the various ways that household drinking water was stored revealed that 98% of the population stored their drinking water within the house and that 99.5% of them provided covers (tops) for containers. The storage container was either an earthenware pot, metal drum or bucket when stored unrefrigerated, and plastic or glass when refrigerated. The increase in the infection rate associated with 2 to 3 days storage could be due to increased ingestion of cysts that matured later with prolonged storage under such conditions that their viability was maintained. The decrease in the infection rate associated with longer periods of storage could be due to loss of viability of most cysts with settling out at the bottom of the con-
Downloaded from http://ije.oxfordjournals.org/ at Monash University on June 20, 2015
DISCUSSION Our results show 11.2% of the Metropolitan Lagos population infected with Entamoeba kistolytica. Unlike earlier studies in Lagos, this estimate is based on a population sample. The prevalence of infection was 10.6% for males and 11.5% for females, an insignificant difference statistically. Male and female rates were similar and increased consistently up to age 35. Thereafter the lower rates for women in age groups most likely reflect different exposure to infection: the low rate in the oldest males reflects poorer cooperation with provision of fewer samples of faeces. It is perhaps not surprising to find that the infection rate differed between ethnic groups. Although some of the variation is due to the small numbers examined it is likely that genuine differences exist. It is also likely that the majority of infections were acquired within the metropolis, but the results do not show an effect of overcrowding. A previous study (3) found higher rates of infection with overcrowding, but our methodology was different. Only a few members of each household were randomly selected. It is possible that the effect of overcrowding would have been more pronounced had all members of every family been examined. The response from the highly educated members of the population to request for specimen of faeces was poor, hence a meaningful comparison of the rate of infection in relation to standard of education cannot be made. Only 4 and 5 people with University education and teacher training respectively, and 27 and 31 people in the senior and intermediate categories respectively were examined. Nevertheless, the mere fact that some were found to be infected is an indication that infection might still be a problem in these groups. The infection rate increased in the wet season, reaching a peak in the last month. Although no infection was recorded in June, this may be due to the small numbers (6) of people examined; if more people had been examined, some infections might have been found. A number of reasons may explain
the fluctuations in the rate of infection. During the later months of the wet season, the temperature is high, and humidity is at its highest. Under conditions of high temperature and humidity, Entamoeba histolytica cysts mature within a short time and also remain viable for a long time (4). Following the peak period of infection at the change of the seasons, the infection rate decreased. During this period although the temperature remains high, the humidity is much lower. Under such conditions the cysts although maturing quickly lose their viability and disintegrate much sooner. This results in fewer mature (infective) cysts available for ingestion. The on-set of the rains is accompanied by a decrease in temperature. This results in disintegration of most cysts before they mature and may account for the very low infection rate in the middle of the wet season. A similar finding was reported by Obiamiwe (5) who observed that Entamoeba bistolytica and other cyst forming protozoa have their peak periods of infection when both temperature and humidity are high. He attributed the high rate of infection to increased contamination from flies.
ENTAMOEBA HISTOLYTICA INFECTION IN NIGERIA
59
REFERENCES (1) Oyerinde J P O, Ogunbi O and Alonge A A. Age and sex distribution of infections with Entamoeba bistolytica and Giardia intestinalis in the Lagos Population. International Journal of Epidemiology 6. 231, 1977. (2) Morgan R W and Kannistro V. A population dynamics survey in Lagos, Nigeria. Social Science and Medicine 7. 1, 1973. (3) Spence H C Jr, Hermos J A, Healy G R, Melvin D M and Schmuncs E. Endemic amoebiasis in Arkansas community. American Journal of Epidemiology 1 0 4 . 9 3 , 1976. (4) Davey T H and Wilson T. Davey and Lightbody's the control of disease in the tropics. 4th Edition p 49. The English Language Society and H K Lewis & Co Ltd, 1971. (5) Obiamiwe B A. The Pattern of parasitic infection in human gut at the Specialist Hospital, Benin City, Nigeria. Annals of Tropical Medicine and ParasitologylU 35, 1977.
(Revised version received 25 May 1978)
1979 Graduate Summer Session in Epidemiology — University of Minnesota The Fourteenth Graduate Summer Session in Epidemiology sponsored by the Epidemiology Section of the American Public Health Association, the Association of Teachers of Preventive Medicine and the American College of Preventive Medicine will be presented at the University of Minnesota in Minneapolis through the School of Public Health, Health Sciences Center and the Nolte Center for Continu-
ing Education during the three-week period from June 17 to July 7, 1979. Further information and application forms for the 1979 session may be obtained by writing to Dr Leonard M Schuman, Director, Graduate Summer Session in Epidemiology, University of Minnesota School of Public Health, 1-117 Health Science Unit A, 515 Delaware St, SE, Minneapolis, Minnesota 55455, USA.
Downloaded from http://ije.oxfordjournals.org/ at Monash University on June 20, 2015
tainer. Thus it appears that in metropolitan Lagos, the source of water per se is of little significance in the transmission of Entamoeba bistolytica but the various treatments that household water is subjected to play a major role in the ability of the water to transmit the parasite. The difference between the prevalence of infection among those who deposited faeces in buckets and in pits and those using water closets might be due to a difference in general hygiene. The pits and buckets are usually situated in close proximity to homes and such facilities are usually open to flies and other insects which are efficient mechanical carriers of Entamoeba bistolytica cysts. Thus, some of the infection might be acquired through contamination of food by flies. The high rates of infection among various food handlers identify a risk to which most members of the population, irrespective of their status, are at times exposed. This finding, together with an appreciation of other factors contributing to Entamoeba bistolytica infection, identifies directions for public health activity.
COMMUNITY MEDICINE The Journal of the Faculty of Community Medicine of the Royal Colleges of Physicians of the United Kingdom. This new quarterly journal represents in an authoritative and distinctive manner the whole range of theory and practice of Community Medicine and its related disciplines in both the United Kingdom and Overseas.
Original papers are invited to be submitted for publication and should be between 2000 and 5000 words in length. Technical requirements are based on The Declaration of Vancouver' (British Medical Journal 20.5.78 p. 1334 ff). Further advice may be obtained from the Editors to whom two copies of contributions should be sent addressed to The Editors, Community Medicine, c/o John Wright and Sons Ltd., 42-44 Triangle West Clifton, Bristol BS8 1 EX. The journal is published quarterly beginning in February 1979 at £12.50 (U.K. & Eire), £15.00 (Overseas), and subscriptions should be sent to Community Medicine, John Wright & Sons Ltd., 42-44 Triangle West Clifton, Bristol BS8 1 EX.
Publication
The Journal of Infection
Quarterly, from March 1979 Subscription
Volume 1 £16.00 (UK) $42.50 (Overseas) Prices include postage Infection, resulting from the interaction of host and microbe, is found in a multitude of different forms, both in man and animals. The journal will reflect this diversity as the editorial policy is to publish not only contributions on clinical infection in man and animals, but also on microbiological, immunological, therapeutic, epidemiological, haematological and statistical aspects of the subject. From time to time there will be an in-depth study of a special topic in infection. There will also be book reviews and a correspondence column.
Academic Press London
New York
San Francisco
A Subsidiary of Harcourt Brace Jovanovich, Publishers 24-28 Oval Road, London NW1, England 111 Fifth Avenue, New York, NY 10003, USA
Downloaded from http://ije.oxfordjournals.org/ at Monash University on June 20, 2015
Fields to be covered by the journal: Epidemiology; demography; medical statistics; operational and health services research; health economics; the social and behavioural sciences; law, ethics, history and general economics as related to community medicine; health information systems and computers; management and administration of health services; preventive medicine; environmental health; clinical community health; health education; occupational medicine; aspects of paediatrics and developmental medicine, geriatrics, psychiatry, communicable disease, laboratory medicine, genetics and their application.
Vol. 8 No. 1 Printed in Great Britain
The Epidemiology of Entamoeba Histolytica in a Nigerian Urban Population J P O OYERINDE 1 , A A ALONGE, A F ADEGBITE-HOLLIST and O OGUNBI
spread of the parasite. Those who did not reply to any of the questions or whose specimens could not be examined for any reason are not Included in the results.
INTRODUCTION
In Nigeria Entamoeba bistolytica is known to exist in people of both sexes and all age-groups. Transmission of the parasite is closely associated with environmental sanitation, hygiene and personal habits. In a recent communication (1) a prevalence of 9.5% was reported for a segment of the population. This report describes the prevalence of Entamoeba histolytica and possible modes of infection among the various categories of people in the population.
RESULTS Microscopic examination of one to three faeces samples from 2 797 persons revealed infection with Entamoeba bistolytica in 312 (11.2%) - 123 (10.6%) of males and 189 (11.5%) of females. Table 1 gives the age—sex specific prevalence and shows that the infection was more common in older agegroups. Lagos is a cosmopolitan city where every ethnic group in the country is represented. The prevalence in different ethnic groups was very variable ranging from 0.0% among the Itshekiris and the Ijaws to some 25% or more among the Efik, Benin and Urhobo (Table 2). Although the numbers examined in some groups, eg Urhobos, Hausa/Fulani etc were small the proportions represent the composition of the population. To examine whether or not infection was acquired before arriving in Lagos, information was obtained from respondents on their date of arrival. The highest infection rate, 18.4% was in those who had lived in the city continuously for more than 8 years those who had lived in the city for 3, 2 and 1 years had rates of 13.9%, 8.2% and 5.2% respectively.
MATERIALS AND METHODS A total of 2 825 persons consisting of 1 163 males and 1 662 females from 10 sample survey areas of the Metropolitan Lagos, as mapped out by Morgan and Kannistro (2), participated in the study. From one to three stool samples were collected from each person and unformed stools were examined for active trophozoites, as quickly as possible. The rest were then concentrated by the formol-saline-ether technique and examined after staining in iodine. Information was obtained from every subject on his or her eating habit, type of toilet facility, water supply and other factors likely to be concerned in Department of Microbiology and Parasitology, College of Medicine, University of Lagos, PMB 12003, Lagos, Nigeria.
55
Downloaded from http://ije.oxfordjournals.org/ at Monash University on June 20, 2015
Oyerinde JPO (Department of Microbiology and Parasitology, College of Medicine, University of Lagos, PMB 12003, Lagos, Nigeria), Alonge A A, Adegbite-Hollist A F and Ogunbi 0 . The epidemiology of Entamoeba histolytica in a Nigerian urban population. International Journal of Epidemiology 1979, 8: 55—59. Microscopic examination of multiple faeces samples of 2 825 persons was carried out in the Metropolitan Lagos. Overall prevalence of Entamoeba histolytica was 11.2%. Prevalence increased rapidly in younger age groups and there were no real differences between males and females. Prevalence was high among families who ate together from the same plate, among those who ate with their fingers and among those who ate away from home. Prevalence was not associated with type of water supply but was seemingly influenced by storage of household supplies. A low infection rate was associated with the availability of water closets and toilet habit. No association was found between prevalence and standard of education but the rate of infection was increased among workers with high occupational interaction. Significant differences were found among different ethnic groups. The highest infection rate was recorded in the last month of the wet season.
56
INTERNATIONAL JOURNAL OF EPIDEMIOLOGY TABLE 1
Prevalence of Entamoeba bistolytica infection by age-group and sex Males
Age in years Under Vi Vi-\
1-5
6-15 16-25 26-35 36-45 46-55 56+
Tot*!
No Examined*
Total
Females No Examined*
% Positive
% Positive
No Examined*
% Positive
35 42 320 380 132 90 97 37 23
0.0 2.4 6.3 11.1 14.3 16.6 16.4 18.9 13.0
43 57 314 366 287 220 145 58 51
0.0 1.9 5.7 11.8 13.9 17.7 11.7 12.0 23.5
78 99 634 846 419 310 242 95 74
0.0 2.0 6.0 11.5 14.0 17.4 13.6 14.7 20.2
1156
10.6
1641
11.5
2797
11.2
TABLE 2
Prevalence of Entamoeba bistolytica by ethnic groupings and sex No Examined*
Yoruba Hausa/Fulani Ibo Benin Itshckiri Urhobo Efik Ijaw Other Nigerian
2534 15 92 15 35 6 33 47 21
infection
Positive 11.2 13.3 16.3 26.7 0.0 33.3 24.2 0.0 4.8
number excludes those who did not respond to this question and/or whose results could not be recorded for various reasons TABLE 3
Influence of education on prevalence of Entamoeba bistolytica infection —No Examined*
University Teacher Training Trade or commercial Vocational/professional Secondary Modern Primary Private No formal education
4 5 9 19 264 47 964 37 1158
%
Positive 25.0 40.0 0.0 5.2 17.0 21.2 13.0 5.4 10.0
number excludes those who did not respond to this question and/or whose remits could not be recorded for various reasons
No association was found between size of family and infection: prevalence varied between 7.8% among families with 8 members to 17.8% in the families consisting of only 2 persons. No association was found between standard of education and infection (Table 3). These findings must be interpreted cautiously however in view of the method of sampling and the small numbers of highly educated respondents. Prevalence varied significantly in different occupational groups. A high infection rate was associated with occupations where interaction among the workers was high, semi-skilled 17.9%, unskilled 16.5%, and residual categories 15.1%. The lowest prevalence occurred when occupational interaction was minimal as in the senior category with an infection rate of 7.4%, or where occupational interaction was nil as in the unemployed group (6.7%) and housewives (10.5%). Two types of climate predominate in the country, a wet season between mid-April and mid-October, and a dry season. During the wet season 2 020 people were examined and 218 (10.7%) were infected: in the dry season 576 people were examined and 110 (19.1%) were infected. The monthly rate of infection is shown in Figure 1. The majority of the respondents drank tap water: others drank well or spring water. The infection rate was 12.4% among those who had tap-water in their homes, 10.9% among those who obtained their drinking water from carriers and 10.6% among those who relied on local pump water. The highest rate (23.4%) was in those who drank well water but none of those who relied on spring water were infected. The prevalence in those who
Downloaded from http://ije.oxfordjournals.org/ at Monash University on June 20, 2015
* number excludes those who did not respond to this question and/or whose results could not be recorded for various reasons.
ENTAMOEBA HISTOLYTICA INFECTION IN NIGERIA 30
-
Ihy WET
Jw»
My
Aug.
Stpt
Oct
Nov.
SEASON
Dec.
Jin.
DRY MONTHS
OF
THE
Ftb.
Mn
SEASON
YEAR
Monthly fluctuations in the prevalence of E. bistolytica infections with the prevailing climatic conditions
cleaned their water containers daily was 9.2% and this increased significantly to 12.8% among those who stored their drinking water for 2 days. Following this, prevalence declined with increasing length of storage to 7.1% at 7 days. 15.0% of those who prepared food either for their families or for the public as a profession were infected with Entamoeba bistolytica. The highest infection rate of 39% (16/41) was in those selling uncooked food; one person out of seven examined (14.2%) from among those engaged in food manufacture was infected. The prevalence of infection was 11.8% for those selling cooked food, 8.5% for those involved in food preparation and
4.9% for those whose duty was merely to serve food. A prevalence of 12.3% was found in families whose members ate together from the same plate and 10.5% for those who ate separately. 11.9% of those who ate with their fingers were infected, compared with only 6.8% of those using cutlery. A prevalence of 12.1% was also found among those who ate elsewhere than in their homes as compared to 6.5% for those who only ate at home. An attempt to correlate prevalence with the type of food eaten, that is, whether cooked or uncooked, whether hot, cold or raw, failed as the data were too complex to analyse, mainly because of the diversity within individual diets.
Downloaded from http://ije.oxfordjournals.org/ at Monash University on June 20, 2015
Apr.
FIGURE 1
57
58
INTERNATIONAL JOURNAL OF EPIDEMIOLOGY
An infection rate of 10.7% was associated with the availability of a water closet, while rates among those who deposited faeces in buckets and in pits were 12.1% and 13.4% respectively. Those who gave no specific means of faeces disposal had an infection rate of 9.5%, such people depending either on a neighbour's or the public facilities. 14.6% of those who used water for cleaning after passing faeces were infected, compared with 9.9% of those using toilet papers.
The high prevalence of infection (23.4%) found among those who drank well water could possibly have resulted from the fact that in homes of such people, the pit latrine is the most common means of faeces disposal. The well is usually situated close to the latrine and seepage might occur. Another source of infection might be through the containers used to draw the water. It is also known that coliform bacteria are frequently isolated from bacteriological examination of tap-water which suggests some degree of faecal contamination. This might explain the high prevalence of 12.4% in those who drank tap water. The rate of infection with Entamoeba bistolytica did not differ according to whether respondents used tap water, water brought from carriers or water from the local pump. Investigations into the various ways that household drinking water was stored revealed that 98% of the population stored their drinking water within the house and that 99.5% of them provided covers (tops) for containers. The storage container was either an earthenware pot, metal drum or bucket when stored unrefrigerated, and plastic or glass when refrigerated. The increase in the infection rate associated with 2 to 3 days storage could be due to increased ingestion of cysts that matured later with prolonged storage under such conditions that their viability was maintained. The decrease in the infection rate associated with longer periods of storage could be due to loss of viability of most cysts with settling out at the bottom of the con-
Downloaded from http://ije.oxfordjournals.org/ at Monash University on June 20, 2015
DISCUSSION Our results show 11.2% of the Metropolitan Lagos population infected with Entamoeba kistolytica. Unlike earlier studies in Lagos, this estimate is based on a population sample. The prevalence of infection was 10.6% for males and 11.5% for females, an insignificant difference statistically. Male and female rates were similar and increased consistently up to age 35. Thereafter the lower rates for women in age groups most likely reflect different exposure to infection: the low rate in the oldest males reflects poorer cooperation with provision of fewer samples of faeces. It is perhaps not surprising to find that the infection rate differed between ethnic groups. Although some of the variation is due to the small numbers examined it is likely that genuine differences exist. It is also likely that the majority of infections were acquired within the metropolis, but the results do not show an effect of overcrowding. A previous study (3) found higher rates of infection with overcrowding, but our methodology was different. Only a few members of each household were randomly selected. It is possible that the effect of overcrowding would have been more pronounced had all members of every family been examined. The response from the highly educated members of the population to request for specimen of faeces was poor, hence a meaningful comparison of the rate of infection in relation to standard of education cannot be made. Only 4 and 5 people with University education and teacher training respectively, and 27 and 31 people in the senior and intermediate categories respectively were examined. Nevertheless, the mere fact that some were found to be infected is an indication that infection might still be a problem in these groups. The infection rate increased in the wet season, reaching a peak in the last month. Although no infection was recorded in June, this may be due to the small numbers (6) of people examined; if more people had been examined, some infections might have been found. A number of reasons may explain
the fluctuations in the rate of infection. During the later months of the wet season, the temperature is high, and humidity is at its highest. Under conditions of high temperature and humidity, Entamoeba histolytica cysts mature within a short time and also remain viable for a long time (4). Following the peak period of infection at the change of the seasons, the infection rate decreased. During this period although the temperature remains high, the humidity is much lower. Under such conditions the cysts although maturing quickly lose their viability and disintegrate much sooner. This results in fewer mature (infective) cysts available for ingestion. The on-set of the rains is accompanied by a decrease in temperature. This results in disintegration of most cysts before they mature and may account for the very low infection rate in the middle of the wet season. A similar finding was reported by Obiamiwe (5) who observed that Entamoeba bistolytica and other cyst forming protozoa have their peak periods of infection when both temperature and humidity are high. He attributed the high rate of infection to increased contamination from flies.
ENTAMOEBA HISTOLYTICA INFECTION IN NIGERIA
59
REFERENCES (1) Oyerinde J P O, Ogunbi O and Alonge A A. Age and sex distribution of infections with Entamoeba bistolytica and Giardia intestinalis in the Lagos Population. International Journal of Epidemiology 6. 231, 1977. (2) Morgan R W and Kannistro V. A population dynamics survey in Lagos, Nigeria. Social Science and Medicine 7. 1, 1973. (3) Spence H C Jr, Hermos J A, Healy G R, Melvin D M and Schmuncs E. Endemic amoebiasis in Arkansas community. American Journal of Epidemiology 1 0 4 . 9 3 , 1976. (4) Davey T H and Wilson T. Davey and Lightbody's the control of disease in the tropics. 4th Edition p 49. The English Language Society and H K Lewis & Co Ltd, 1971. (5) Obiamiwe B A. The Pattern of parasitic infection in human gut at the Specialist Hospital, Benin City, Nigeria. Annals of Tropical Medicine and ParasitologylU 35, 1977.
(Revised version received 25 May 1978)
1979 Graduate Summer Session in Epidemiology — University of Minnesota The Fourteenth Graduate Summer Session in Epidemiology sponsored by the Epidemiology Section of the American Public Health Association, the Association of Teachers of Preventive Medicine and the American College of Preventive Medicine will be presented at the University of Minnesota in Minneapolis through the School of Public Health, Health Sciences Center and the Nolte Center for Continu-
ing Education during the three-week period from June 17 to July 7, 1979. Further information and application forms for the 1979 session may be obtained by writing to Dr Leonard M Schuman, Director, Graduate Summer Session in Epidemiology, University of Minnesota School of Public Health, 1-117 Health Science Unit A, 515 Delaware St, SE, Minneapolis, Minnesota 55455, USA.
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tainer. Thus it appears that in metropolitan Lagos, the source of water per se is of little significance in the transmission of Entamoeba bistolytica but the various treatments that household water is subjected to play a major role in the ability of the water to transmit the parasite. The difference between the prevalence of infection among those who deposited faeces in buckets and in pits and those using water closets might be due to a difference in general hygiene. The pits and buckets are usually situated in close proximity to homes and such facilities are usually open to flies and other insects which are efficient mechanical carriers of Entamoeba bistolytica cysts. Thus, some of the infection might be acquired through contamination of food by flies. The high rates of infection among various food handlers identify a risk to which most members of the population, irrespective of their status, are at times exposed. This finding, together with an appreciation of other factors contributing to Entamoeba bistolytica infection, identifies directions for public health activity.
COMMUNITY MEDICINE The Journal of the Faculty of Community Medicine of the Royal Colleges of Physicians of the United Kingdom. This new quarterly journal represents in an authoritative and distinctive manner the whole range of theory and practice of Community Medicine and its related disciplines in both the United Kingdom and Overseas.
Original papers are invited to be submitted for publication and should be between 2000 and 5000 words in length. Technical requirements are based on The Declaration of Vancouver' (British Medical Journal 20.5.78 p. 1334 ff). Further advice may be obtained from the Editors to whom two copies of contributions should be sent addressed to The Editors, Community Medicine, c/o John Wright and Sons Ltd., 42-44 Triangle West Clifton, Bristol BS8 1 EX. The journal is published quarterly beginning in February 1979 at £12.50 (U.K. & Eire), £15.00 (Overseas), and subscriptions should be sent to Community Medicine, John Wright & Sons Ltd., 42-44 Triangle West Clifton, Bristol BS8 1 EX.
Publication
The Journal of Infection
Quarterly, from March 1979 Subscription
Volume 1 £16.00 (UK) $42.50 (Overseas) Prices include postage Infection, resulting from the interaction of host and microbe, is found in a multitude of different forms, both in man and animals. The journal will reflect this diversity as the editorial policy is to publish not only contributions on clinical infection in man and animals, but also on microbiological, immunological, therapeutic, epidemiological, haematological and statistical aspects of the subject. From time to time there will be an in-depth study of a special topic in infection. There will also be book reviews and a correspondence column.
Academic Press London
New York
San Francisco
A Subsidiary of Harcourt Brace Jovanovich, Publishers 24-28 Oval Road, London NW1, England 111 Fifth Avenue, New York, NY 10003, USA
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Fields to be covered by the journal: Epidemiology; demography; medical statistics; operational and health services research; health economics; the social and behavioural sciences; law, ethics, history and general economics as related to community medicine; health information systems and computers; management and administration of health services; preventive medicine; environmental health; clinical community health; health education; occupational medicine; aspects of paediatrics and developmental medicine, geriatrics, psychiatry, communicable disease, laboratory medicine, genetics and their application.
