Editorial

Vol. 11. No. 2

95

Eur. J. Clin. Microbiol. Infect. Dis., February 1992, p. 95-98 0934-9723/92/02 0095-04 $ 3.00/0

Prevalence Studies in Nosocomial Infections*

R.C. Spencer

Nosocomial infections represent an important public health problem in the world today (1, 2). The nationwide nosocomial infection rate in the USA was estimated to be 5.7 nosocomial infections per 100 admissions to acute care hospitals between 1975 and 1976; this is more than the number of hospital admissions for either cancer or accidents and at least four times greater than admissions for acute myocardial infarction (2), Prevalence surveys have indicated a variation in prevalence rates of nosocomial infection from 6.1 to 17 % (3-10). Urinary tract, Wound and respiratory infections are the commonest types of nosocomial infection (3, 5, 6, 8). Mortality related to nosocomial infections is highly significant (2), and the cost of excess hospitalization caused by nosocomial infections in the USA was estimated at $ 2.38 billion per year in 1981 (1). In countries where the average duration of hospitalisation is longer than in the USA, as in many European COUntries, the risks of acquiring infection are increased. In 1982 it was estimated that decreasing the infection rate by 10 to 24 % in Germany would result insavings of DM 63 to 800 million per year (11). The past few years have seen a rapid growth in an!imicrobial resistance, an increase in patients with impaired immunity, a growing emphasis on the Use of technology and instrumentation, the recognition of new organisms causing infection, and an Increasing focus on cost control (12). The costs, morbidity and mortality related to nosocomial infections can only be expected to increase in the future. The prevention and control of nosocomial infections is, therefore, of growing importance. Staphylococcal infections may, once more, play a part in precipitating a growth in nosocomial infection prevention and control programmes. The evolution of methicillin-resistant Staphylococcus Department of Experimental and Clinical Microbiology, Royal blallarnshire Hospital, Glossop Road, Sheffield, UK. *The attention of readers is drawn to the single-day Po~evalence study to be conducted in 17 centres in Europe zy April 1992. For more information refer to the announcements section at the end of the journal.

aureus (MRSA) has contributed to the resurgence of staphylococcal infections as a major hospital problem (12). The staphylococcal pandemic in the late 1950s demonstrated the need for an organized infection control effort; it was not until the early 1970s, however, that this need was translated into action in the USA, with a dramatic increase in the number of hospitals initiating infection control programmes.

The act of systematically collecting, tabulating and analysing data on the occurrence of nosocomial infections became known as "surveillance," and by the end of the 1970s the majority of US hospitals had jumped on the "surveillance bandwagon" (13). The early 1980s saw an increasing disillusionment with routine comprehensive hospital-wide surveillance, which has been described as "time-consuming activities in search of objectives" (13), and the growth of the concept of "targeted surveillance" or "surveillance by objective" (13,14). Like the philosophy of corporate management, the objectives of surveillance should be to achieve defined measures of process and outcome: measures of what is actually done to achieve the final desired outcome. Some examples of outcome objectives have been described: to reduce the risks of nosocomial infections; to reduce patients' suffering and inconvenience; and to reduce the costs to the patient, the hospital, and the health care system (13). Various types of surveillance programmes have evolved over the past 30 years (1). Most were developed in the USA, where interest in infection control was stimulated by the Centers for Disease Control (CDC), Atlanta, Georgia (15). In the 1960s the CDC recommended that hospitals initiate surveillance programmes in order to obtain epidemiotogical evidence on which to base rational infection control measures (15). Early comprehensive data collection forms gave way to more specific reviews of the microbiology records and autopsy reports (1). More recently, other methods of surveillance have been used, including the prevalence survey. A prevaIence survey provides data about hospitalized patients or hospital records at one point in

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time (16). In general, only those infections judged to be clinically active at the time of screening are recorded. The outcome is recorded as the proportion of all patients screened who had active nosocomial infections at the time of screening (16). In contrast, an incidence survey provides data on sequential admissions to or discharges from hospitals (16). Incidence surveys are usually performed by studying the records after discharge or, rarely, during hospitalization. The strict definition of incidence is the number of new cases of nosocomial infection that occur per unit population at risk over a given period of observation (16). Many incidence surveys have been criticized for not reporting the strict incidence according to this definition. Instead, the more comprehensible "attack rate" is used: the proportion of exposed individuals who become infected over the entire period of exposure or duration of hospitalization (16). Both types of survey have been shown to be effective methods of surveillance in terms of achieving some of the outcome objectives defined above (4, 15, 17). The choice of surveillance method or methods used in each hospital should reflect the following: the types and incidences of nosocomial infections found; the types of patients admitted; the size and type of hospital; the support services available within the hospital; and the desired outcome objectives (1,13). There is, therefore, a need for hospitals to conduct their own surveillance in order to develop appropriate infection control and prevention programmes (17). A prevalence survey has several general advantages over an incidence study. Prevalence surveys are easier, cheaper and less time-consuming to perform than incidence studies (8); they also provide quantitative information about nosocomiai infections which is easy to obtain and which can help to boost awareness of the problems associated with these infections (8, 9). Convincing hospital staff of the scale of a problem is an important stage in the introduction of any new policy infection control policies are no exception. It is generally easier to administrate a prevalence survey because it takes less time than an incidence study, and this may contribute to a greater likelihood of survey accuracy (8). Prevalence surveys easily incorporate a bedside examination of the patient and, therefore, relevant clinical information, whereas incidence studies are usually retrospective (16). Results derived from incidence and prevalence surveys are not directly comparable because

Eur. J. Clin. Microbiol. Infect. Dis.

slightly different parameters are measured (8). Incidence rates of nosocomial infection average about 5 % and prevalence rates about 10 % in the USA (17). In a study using the same hospital population, the average duration of stay in hospital was found to be 13.3 days when a prevalence survey was conducted and 7.3 days from a corresponding incidence survey (18). Prevalence surveys take into account the change in the period of time that infected patients stay in hospital and, therefore, reflect some of the added cost of nosocomial infection (8). The resultant data allow the best estimates of the burden imposed on the health care system by nosocomial infection (9). Prevalence surveys can be used more directly to measure some of the costs of nosocomial infection. Data from seven single-day prevalence surveys, conducted between 1986 and 1989 in a hospital in Hong Kong, were used to assess the costs of nosocomial infection by matching infected cases with controls (17). Details of mortality, length of hospitalization and antibiotic costs were used as measures of the costs of nosocomial infection. Infected patients were found to have an excess mortality rate of 7.4 %, an average excess hospital stay of 23 days and an average excess antibiotic expenditure of US $190. The annual costs of potentially avoidable nosocomial infections were calculated at 130 lives, 42,000 bed days and US $ 0.3 million of antibiotics in this hospital. In comparison, the cost of instituting an infection control programme at this hospital was estimated to be about 1.25 % of the potential savings; it would thus be a highly cost-effective measure. In Australia, the first national nosocomial prevalence study, prompted by the need to collect data on surgical wound infection relevant to the Australian population, estimated that surgical wound infections cost about $ 60 million in 1984 (19). The efficacy of infection control policies can be easily measured by repeated prevalence surveys (4, 5). Two single-day prevalence surveys in 1985 and 1986 were conducted by a team of seven to nine trained staff in a Hong Kong hospital. An infection control policy was then introduced and further single-day prevalence studies performed. The prevalence of nosocomial infection was found to fall linearly from 10.5 % pre-policy to 5.6 % post-policy. In addition, a specific significant decrease in the prevalence ofnosocomial urinary tract infection was found after the introduction of a catheter-care infection control policy. These differences persisted when the results were adjusted for patient risk factors for nosocomial in-

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fection. Repeated prevalence surveys can thus provide practical and sensitive methods of measuring nosocomial infection and can be used to assess the impact of infection control programmes (4). Incidence surveys can, of course, also be used to assess the efficacy of infection control policies. One of the aims of the SENIC Project (Study on the Efficacy of Nosocomial Infection Control), initiated in the USA in 1974, was to determine whether organized surveillance resulted in a reduced nosocomial infection rate (15). The SENIc Project, a retrospective study of the inC!dence of nosocomial infection, found that intenSive infection surveillance and control programrues were associated with a reduction in the rates of nosocomial urinary tract and surgical wound infections, pneumonia and bacteraemia (4, 15). Nosocomial infections were reduced by approximately one-third in hospitals where intenswe infection surveillance existed (15). Prevalence surveys can indicate clinical areas and procedures associated with a high risk of nosocomial infection. In Australia, specific data from a prevalence survey on infection rates for different types of surgery led to calls for specific preventive interventions and the introduction of control and SUrveillance programmes (19). Special care baby units and genitourinary surgical departments Were highlighted as areas of particular risk of nosocomial infection in a prevalence survey in England and Wales (8): specific investigations designed to identify, measure and possibly control the factors leading to this increased risk were Specified as necessary. Patients admitted to intensive care units (ICUs) have a higher risk of nosocomial infection than Other hospitalized patients (7, 20, 21). Compared ith general medical/surgical ward patients, who ave been found to have a 6 % overall risk of acquiring an infection during their hospital stay, critically ill patients in the ICU have been found to have an 18 % risk (20). Nosocomial infections are more frequent in ICUs because of the severity of the Underlying disease, the duration of hospital ltay, the use of invasive procedures, contaminated ~e-support equipment, crowding, and the preValence of resistant microorganisms (22).

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The risk of acquiring a nosocomiai infection inCreases with the length of stay in the ICU and with device Utilization (23), and infections are one of e most frequent causes of death in ICUs (24). oSocomial infections vary in frequency and type between different ICUs (22), and knowledge of

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the patterns of nosocomial infection is of value in the adoption of appropriate infection control policies within an ICU (22). Furthermore, infection control programmes have been shown to reduce the rate of nosocomial infections in ICUs (24). Targeted surveillance and the subsequent initiation of appropriate infection control measures in ICUs is, therefore, likely to result in lower morbidity and mortality related to nosocomial infections and to be cost-effective. Most of the studies of nosocomial infection focussing specifically on intensive care have to date been carried out in the USA; European prevalence studies have tended to examine hospitalwide rates of nosocomial infections. On 29 April 1992 a single-day prevalence study of infection in ICUs in 17 countries in Europe will take place. Information will be collected on the demographics of ICUs, infection control resources and procedures, antibiotic policies and prescribing, patient outcome, and associated risk factors for infection. The EPIC Study, the European Prevalence of Infection in Intensive Care Study, will help to raise awareness of the problems of infection in the ICU and will provide a targeted surveillance programme through which infection control policies can be rationalized. This study will be the largest of its kind ever undertaken and is likely to provide the basis for increased collaborative efforts in infection control. It is hoped that this study will provide the roots for a European perspective on nosocomial infections in ICUs and will begin to establish some solutions to a growing problem.

References

1. Brachnmn PS: Nosocomial infection control: an overview. Reviewsof Infectious Diseases 1981, 3: 640--648. 2. ltaley RW, Culver DH, While JW, Morgan WM,

Emori TG: The nationwide nosocomial infection rate: a new need for vital statistics. American Journal of Epidemiology 1985, 121: 159-167. 3. ~ralmovfi, Bartofiov~i A, Bolek S, Kre~merov~i M, ~uberlovfi V: National prevalence survey of hospitalacquired infections in Czechoslovakia. Journal of Hospital Infection 1988, i1: 328--334. 4. French GL, Cheng AFB, Wong SL, Donnan S:

Repeated prevalence surveys for monitoring effectiveness of hospital infection control. Lancet 1989, ii: 10211023. 5. French GL, Cheng A, Farrington M: Prevalence survey of infection in a Hong Kong hospital using a standard protocol and microcomputer data analysis. Journal of Hospital Infection 1987, 9: 132-142. 6. Jepsen OB, Morlensen N: Prevalence of nosocomial infection and infection control in Denmark. Journal of Hospital Infection 1980, 1: 237-244,

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7. Moro ML, Stazi MA, Marasca G, Greco D, Zampieri A: National prevalence survey of hospital-acquired infections in Italy, 1983. Journal of Hospital Infection 1986, 8: 72-85.

8. Meers PD, Ayliffe GAJ, Emmerson AM, Leigh DA, Mayon.White RT, Mackintosh CA, Stronge JL: Report on the national survey of infection in hospitals, 1980. Journal of Hospital Infection 1981, 2, Supplement: 1-51.

9. Mertens R, Kegels G, Stroobant A, Reybrouck G, Lamotte JM, Potvliege C, Van Casteren V, Lauwers S, Verschraegen G, Wauters G, Minne A, Thiers G: The national prevalence survey of nosocomial infections in Belgium, 1984. Journal of Hospital Infection 1987, 9: 219-229. 10. Bernander S, Hambraeus A, Myrbfick K-E, Nystr6m B, Sundeliif B: Prevalence of hospital-associated infections in five Swedish hospitals in November 1975. Scandinavian Journal of Infectious Diseases 1978, 10: 66-7O. 11. Daschner F: Economic aspects of hospital infections. Journal of Hospital Infection 1982, 3: 1-4. 12. McGowan JE: Antibiotic resistance in hospital bacteria: current patterns, modes for appearance or spread, and economic impact. Reviews in Medical Microbiology 1991, 2: 161-169. 13. Haley RW: Surveillance by objective: a new prioritydirected approach to the control of nosocomial infections. American Journal of Infection Control 1985, 13: 78-89. 14. Daschner F: Cost-effectiveness in hospital infection control - lessons for the 1990s. Journal of Hospital Infection 1989, 13: 325-336.

15. Haley RW, Culver DH, White JW, Morgan WM, Emori TG, Munn VP, Hooton TM: The efficacy of infection surveillance and control programs in preventing nosocomial infections in US hospitals. American Journal of Epidemiology 1985, 121: 182-205.

16. Freeman J, McGowan JE: Methodologic issues in hospital epidemiology. I. Rates, ease-finding, and interpretation. Reviews of Infectious Diseases 1981, 3: 658-667. 17. French GL, Cheng AFB: Measurement of the costs of hospital infection by prevalence surveys. Journal of Hospital Infection 1991, 18, Supplement A: 65-72. 18. Freeman J, McGowan JE: Mcthodologie issues in hospital epidemiology. III. Investigating the modifying effects of time and severity of underlying illness on estimates of cost of nosocomial infection. Reviews of Infectious Diseases 1984, 6: 285-300.

19. HcLaws M-L, lrwig LM, Mock P, Berry G, Gold J: Predictors of surgical wound infection in Australia: a national study, Medical Journal of Australia 1988, 149: 591-595. 20. Donowitz LG, Wenzei RP, Hoyt JW: High risk of hospital-acquired infection in the ICU patient. Critical CareMedicine 1982, 10: 355-357. 21. Wenzel RP, Thompson RL, Landry SM, Russell BS, Miller PJ, Ponce de Leon S, Miller GB: Hospitalacquired infections in intensive care unit patients: an overview with emphasis on epidemics. Infection Control 1983, 4: 371-375.

22. Pranalharthi H, Chandrasekar MD, Kruse JA, Mathews MF: Nosocomial infection among patients in different types of intensive care units at a city hospital. Critical Care Medicine 1986, 14: 508-510.

23. Jarvis WR, Edwards JR, Culver DH, Hughes JM, Horan T, Emori TG, Banerjee S, Tolson J, Henderson T, Gaynes RP, Martone WJ: Nosocomial infection rates in adult and pediatric intensive care units in the United States. American Journal of Medicine 1991, 9t, Supplement 3B: 185-191. 24. Daschner FD, Frey P, Wolff G, Baumann PC, Surer P: Nosocomial infections in intensive care wards: a multicenter prospective study. Intensive Care Medicine 1982, 8: 5-9.

Prevalence studies in nosocomial infections.

Editorial Vol. 11. No. 2 95 Eur. J. Clin. Microbiol. Infect. Dis., February 1992, p. 95-98 0934-9723/92/02 0095-04 $ 3.00/0 Prevalence Studies in...
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