Public Health Briefs
data available from both years, a reduced model was then considered that contained only hospital PCP volume as the independent variable (Table 2). Results from that model indicated a positive association between hospital PCP volume and percentage HIV identified ( = 0.93, SE = 0.45, p = .049).
Discussion After correcting for the non-HIVrelated PCP discharges, we have found undercoding of HIV infection in discharge abstracts of PCP-identified patients in New York State's acute care facilities. The amount of undercoding was a function of the facility's volume of PCP patients. Our estimate of HIV-related PCP discharges depended on our assumption that the number of non-HIV-related PCP discharges was essentially constant statewide between 1980 and 1988. The results from our review of PCP occurrence in counties with a low incidence ofAIDS and in hospitals with a high occurrence of PCP are consistent with such an assumption. However, there may be secular trends in non-HIV-related causes of PCP that affect the background level. Review of diagnoses in the SPARCS records of nonHIV-identified PCP patients is not sufficient to determine the presence or absence of HIV infection.
o:........:.
|bXjae~ ~ ~ ~ ~ ~ .- . .....
.........,ee....
....
.s
Introdufion
iuaelIbe-w_192au1i9S7acorl Al:'S u wlhnee
ng pro-19SS te .-s.
.°....... ..............!
_
Bnf%4,nhinareM|edfcl
113, So12NgS3333.S333 ....-!.!fff f.!
SSins ""'eS*S''' de.,,,',".Sss,
S'''-SSSS''''''S .....................} '
--S
'S
'S
::-
:}:-x :X
.: :g : : :: 5: : 55 : :g : S : : : :: ... .:: .-.. .:...... ,SS.,,,fiRKion
y: .'-SS ': 'SSS:::'''SpSSS::::} S:: :'SS::K'ithapdniw
d
This research was supported in part by Grant U62/CCU202061-05 from the Centers of Disease Control.
References 1. Statewide Planning and Research Cooperative System (SPARCS), Bureau of Production Systems Management, New York State Department of Health, Corning Tower, Room 1161, Albany, NY 12237. 2. Changes to the International Classification of Diseases, Ninth Rev., Clinical Modification (ICD-9-CM). Federal Register 1986; 51:30914-15. 3. World Health Organization Collaboration Center for Classification of Diseases for North America: HTLV-III/LAV Infection Codes, Official Authorized Addendum Effective October 1, 1986, for the International Classification of Diseases, Ninth Rev., Clinical Modification. Washington, DC: Su of US Government Printing Office 1986. 4. Levine SJ, White DA: Pneumocystis carini. Clin Chest Med 1988; 9:395-423. 5. Stover DE, White DA, Romano PA, et at Spectrum of pulmonary diseases associated with the acquired immunodeficiency syndrome. Am J Med 1985; 78:429-437. 6. Kovacs JA, Hiemenz JW, Macher AM, et at Pneumocystis carinii pneumonia: a comparison between patients with the acquired immunodeficiency syndrome and patients with other immunodeficiencies. Ann Intern Med 1984; 100:663-671. 7. Bureau of Communicable Disease Control, New York State Department of Health: AIDS surveillance monthly update, March 1989. 8. SAS/STAT Users Guide, Release 6.03 Ed. Cary, NC: SAS Institute, 1988; 773-876.
Wliam E. Laffety, MD, David Glidden, BA, and Sharon G. Hopkins, DVM, MPH
S ssa:
(A'I'S)"" 'W' ' ' SoS esse
Acknowledgment
Survival Trends of People with AIDS in Washington State
. . . . . . . . -. -. -.-.-. .-.-.-. . . . . . . . . . . . .
':-.' .
-o..............
The reasons for the hospital variations in reporting PCP patients as HIV infected are unknown. In the interest of confidentiality, a hospital may choose to report that a patient was not HIVpositive even though the condition was diagnosed or suspected. A lack of sufficient number of diagnostic fields in SPARCS may also be a factor, since many PCP patients are sufficiently ill with other conditions that could fill the principal and four secondary diagnosis fields of the SPARCS record. However, since the inclusion of an HIV diagnostic code would increase reimbursement substantially, HIV coding should take precedence by hospitals when its presence is known. Another explanation is that even at this late date in the HIV epidemic, providers in New York State do not recognize that PCP patients demonstrate the most publicized HIV-related opportunistic infection. If so, other, more subtle sequelae of HIV infection maybe being identified at an even lower rate, and treatment of HIVinfected patients may be delayed. Further study of the non-HIV-infected PCP patients would clearly be fruitful. In the absence of such a study, it is prudent to recognize that statewide HIV hospitalization utilization may be underestimated when SPARCS or a comparable system is used as the source. El
:-
In Seattle-King County, the major metropolitan area in Washington State, acquired immunodeficiency syndrome (AIDS) was the third leading cause of death in males aged 25-44years in 1986. In 1987, it was second, according to the King County Department of Vital Statistics. While AIDS continues to increase in importance as a cause of mortality,1 therapeutic advances should eventually be reflected in decreased mortality and longer survival times. Such trends have been reported from major epicenters of the epi-
}>:.-::.:.
demic, such as San Francisco,2 and may be occurring nationwide.3 Our study confirms that survival times of persons living
Address reprint requests to William E. Lafferty, Office of Epidemiology and Surveillance, HIV/AIDS and Infectious Diseases, Washington State Department of Health, 1610 N.E. 150th St., Seattle, WA 98155-7224. Mr. Glidden is with the Biostatistics Department of the University of Washington. Dr. Hopkins is with the Seattle-King County Department of Public Health. This paper, submitted to the Joumal September 26, 1989, was revised and accepted for publication June 21, 1990.
o'
S:::::: SSS::'' ::S}S:
''-
S:::'
SS:::'SS::-' ::SS: :::.S:.::.-
American Journal of Public Health 217
Public Health Bniefs
with AIDS have increased in Washington State independent of changes in the AIDS case definition.
Medtods The Washington State and SeattleKing County human immunodeficiency virus (HIV)-AIDS epidemiology units maintain [a] registry of case reports that meet the Centers for Disease Control (CDC) surveillance definition of AIDS. All resident cases were investigated. Survival analysis was performed only for patients 13 years of age or older that met the pre1987 case definition.4 Cases with more than one primary diagnosis were classified by hierarchy into one of three categories: Pnewnocystis canndi pneumonia (PCP), other diagnosis without PCP, or Kaposi's sarcoma (KS) alone. Passive AIDS case reporting was estimated to be 96 percent and 88 percent complete in 1986 and 1988, respectively, according to methods previously described.5 In December 1988 all presumed surviving cases diagnosed on or before December 1987 were investigated. Provider contact and telephone surveillance are routine and update mortality status yearly. County vital records were reviewed for recent deaths that were either unknown to providers or may not have reached the state's vital records office. County vital records yielded 10 unreported deaths among 286 persons with AIDS who were presumed living after provider contact.
218 American Journal of Public Health
Three cases lost to follow-up were censored at the last date known to be alive. Cohorts were formed of individuals diagnosed in 1985 or before, individuals diagnosed in 1986, and individuals diagnosed in 1987. The groups were compared by means of nonparametric rank tests for censored data6 after adjusting for primary diagnosis but not for any other prognostic variables. The effect of year and diagnosis was also estimated by fitting the Cox proportional hazards model. Hazard comparisons are relative to cases diagnosed before 1986 with KS and were made using BMDP2L.7 Because of the limited amount of data available on any given subject, our ability to investigate and adjust for prognostic variables was limited. The CDC case report forms record the month and year in which an individual is diagnosed and the day, month, and year of death. Approximate survival times were constructed by assuming that all in-
dividuals were diagnosed on the 15th of the month. For the generalized Wilcoxin test this is equivalent to breaking tied death times (tied if counted in months) in favor of individuals who died later in the month. These approximate death times were also used to produce Kaplan-Meier survival curves using PROC Lifetest8 and to produce the relative hazard estimates.
Resuls Through the end of 1987, 777 adult AIDS cases had been reported; 680 met the pre-1987 AIDS case definition. Seventy-one of these cases died within 1 month of diagnosis. Mean age at the time of diagnosis, racial composition, sex, and transmission category of the three temporal cohorts did not change significantly between the intervals (Table 1). Although the proportion of intravenous drug users (IVDUs) increased from 1 percent to 3
February 1991, Vol. 81, No. 2
Public Health Briefs
percent from 1985 to 1987, only 12 IVDUs were included in the study. Overall, the proportion of cases diagnosed as outpatients increased from 11 percent to 20 percent between 1985 and 1987. Of definitively diagnosed cases of KS, 19 percent, 26 percent, and 68 percent were diagnosed as outpatients before 1986, in 1986, and in 1987, respectively (data not shown). Overall, cases survived a median of 14.4 months (Tables 2 and 3). People with KS survived longer than people with PCP. Both groups survived longer than those with other diagnoses. Survival increased in cases diagnosed in more recent years. Cases of PCP and other diagnoses that were diagnosed during 1989 had longer survival times than those diagnosed in 1986 (p < .001, for each comparison). Most people with KS diagnosed in 1987 were still living. Median survival for inpatient cases with primary diagnoses of PCP increased from 12.4, to 15.8, to 20.8 months for the three time intervals, respectively (p < .0001).
Discussion We believe our ascertainment of deaths was fairly complete. Although recent out-of-state deaths could have been missed by these methods, the impact of these cases would be 5 percent or less. In addition, since completion of this study, cases have been matched to the National Death Index. Only two deaths were detected that were not included in this anal-
ysis. Our data confirm that trends seen in
major epicenters of the AIDS epidemic are occurring elsewhere in the United States. Increases in survival for people with primary diagnoses of PCP could be related to PCP prophylaxis and zidovu-
February 1991, Vol. 81, No. 2
dine therapy. Local zidovudine studies treated approximately 52 residents who had PCP diagnosed in 1986. The lack of increase in the median survival of people with other diagnoses from 1985 to 1986 may reflect their ineligibility for zidovudine studies. Although studies in San Francisco have shown a decrease in median survival for people with KS through 1985 and slight increases during 1986 and 1987,2 our KS cohort diagnosed in 1986 survived longer than those diagnosed during or before 1985. The increase in outpatient diagnoses of KS from 1985 to 1987, from 19 percent to 68 percent, suggests this practice may in part be responsible for our local data. The general availability of zidovudine in March 1987 may be responsible in part for the sharp increases in survival seen in 1987. Exclusion of outpatient diagnoses for people with PCP did not reduce median survival; therefore, earlier diagnosis is an unlikely reason for prolonged survival in this cohort. The impact of prolonged survival of people living with AIDS on the health care system needs evaluation. Although CDC case projections for 1990 and beyond have been reduced in cumulative numbers by 16 percent through 1993,9 increased survival may neutralize the effect of fewer new cases on the health care system. Recent federal registration (H.R. 2310) expanding insurance continuation from 18 to 29 months may make health care more accessible to a larger number of people living with AIDS who survive longer than 18 months. However as the use of zidovudine and other antiviral drugs prolongs survival, health care programs need to provide long-term access to people who are otherwise uninsurable. El
Acknowledgments This study was supported by CDC AIDS Surveillance Grant U62/CCU000993-03. The authors thank the AIDS coordinators at the local public health departments for death certificate review and case reporting; Jeanne Honey and Jan Harwell, MPA, MA, for case investigation; Bob Wood, MD, Noreen Harris, DVM, Cathy Critchlow, PhD, Alan Kristal, PhD, and Michael Smyser, MPH, for manuscript review; and Tim Tyree for manuscript preparation. Excerpts from this paper were presented at the 5th International AIDS Conference, June 1989, in Montreal.
References 1. Kristal AR: The impact of the acquired immunodeficiency syndrome virus on patterns of premature death in New York. JAMA 1986; 255:2306-2310. 2. Lemp GF, Payne S, Neal D, et al: Survival trends for patients with AIDS. JAMA 1990;
263:402-406. 3. Harris JE: Improved short-term survival of AIDS patients initially diagnosedwithPneumocystis cainnu pneumonia, 1984 through 1987. JAMA 1990; 263:397-401. 4. Revision of the CDC surveillance case definition for acquired immunodeficiency syndrome. MMWR 1987; 36(suppl. 2s)3-16. 5. Lafferty W, Hopkins S, Honey J, et al: Hospital charges for people with AIDS in Washington State: Utilization of a statewide hospital discharge data base. Am J Public Health 1988; 78:949-952. 6. Cox DR, Oakes D: Analysis of Survival Data. London: Chapman and Hall, 1984. 7. Hopkins A: Survival analysis with covariates: Cox models. In: Dixon WJ, (ed): BMDP Statistical Software. Berkeley: University of California Press, 1985, 576-594. 8. SAS Institute, Inc: SAS User's Guide: Statistics, Version 5 Ed. Cary, NC: SAS Institute, Inc., 1985:529-557, 1989; 111:41-50. 9. Centers for Disease Control: Estimates of HIV prevalence and projected AIDS cases: Summary of a workshop, October 31November 1, 1989. MMWR 39:110-112, 117-119, February 23, 1990.
American Joumal of Public Health 219
data available from both years, a reduced model was then considered that contained only hospital PCP volume as the independent variable (Table 2). Results from that model indicated a positive association between hospital PCP volume and percentage HIV identified ( = 0.93, SE = 0.45, p = .049).
Discussion After correcting for the non-HIVrelated PCP discharges, we have found undercoding of HIV infection in discharge abstracts of PCP-identified patients in New York State's acute care facilities. The amount of undercoding was a function of the facility's volume of PCP patients. Our estimate of HIV-related PCP discharges depended on our assumption that the number of non-HIV-related PCP discharges was essentially constant statewide between 1980 and 1988. The results from our review of PCP occurrence in counties with a low incidence ofAIDS and in hospitals with a high occurrence of PCP are consistent with such an assumption. However, there may be secular trends in non-HIV-related causes of PCP that affect the background level. Review of diagnoses in the SPARCS records of nonHIV-identified PCP patients is not sufficient to determine the presence or absence of HIV infection.
o:........:.
|bXjae~ ~ ~ ~ ~ ~ .- . .....
.........,ee....
....
.s
Introdufion
iuaelIbe-w_192au1i9S7acorl Al:'S u wlhnee
ng pro-19SS te .-s.
.°....... ..............!
_
Bnf%4,nhinareM|edfcl
113, So12NgS3333.S333 ....-!.!fff f.!
SSins ""'eS*S''' de.,,,',".Sss,
S'''-SSSS''''''S .....................} '
--S
'S
'S
::-
:}:-x :X
.: :g : : :: 5: : 55 : :g : S : : : :: ... .:: .-.. .:...... ,SS.,,,fiRKion
y: .'-SS ': 'SSS:::'''SpSSS::::} S:: :'SS::K'ithapdniw
d
This research was supported in part by Grant U62/CCU202061-05 from the Centers of Disease Control.
References 1. Statewide Planning and Research Cooperative System (SPARCS), Bureau of Production Systems Management, New York State Department of Health, Corning Tower, Room 1161, Albany, NY 12237. 2. Changes to the International Classification of Diseases, Ninth Rev., Clinical Modification (ICD-9-CM). Federal Register 1986; 51:30914-15. 3. World Health Organization Collaboration Center for Classification of Diseases for North America: HTLV-III/LAV Infection Codes, Official Authorized Addendum Effective October 1, 1986, for the International Classification of Diseases, Ninth Rev., Clinical Modification. Washington, DC: Su of US Government Printing Office 1986. 4. Levine SJ, White DA: Pneumocystis carini. Clin Chest Med 1988; 9:395-423. 5. Stover DE, White DA, Romano PA, et at Spectrum of pulmonary diseases associated with the acquired immunodeficiency syndrome. Am J Med 1985; 78:429-437. 6. Kovacs JA, Hiemenz JW, Macher AM, et at Pneumocystis carinii pneumonia: a comparison between patients with the acquired immunodeficiency syndrome and patients with other immunodeficiencies. Ann Intern Med 1984; 100:663-671. 7. Bureau of Communicable Disease Control, New York State Department of Health: AIDS surveillance monthly update, March 1989. 8. SAS/STAT Users Guide, Release 6.03 Ed. Cary, NC: SAS Institute, 1988; 773-876.
Wliam E. Laffety, MD, David Glidden, BA, and Sharon G. Hopkins, DVM, MPH
S ssa:
(A'I'S)"" 'W' ' ' SoS esse
Acknowledgment
Survival Trends of People with AIDS in Washington State
. . . . . . . . -. -. -.-.-. .-.-.-. . . . . . . . . . . . .
':-.' .
-o..............
The reasons for the hospital variations in reporting PCP patients as HIV infected are unknown. In the interest of confidentiality, a hospital may choose to report that a patient was not HIVpositive even though the condition was diagnosed or suspected. A lack of sufficient number of diagnostic fields in SPARCS may also be a factor, since many PCP patients are sufficiently ill with other conditions that could fill the principal and four secondary diagnosis fields of the SPARCS record. However, since the inclusion of an HIV diagnostic code would increase reimbursement substantially, HIV coding should take precedence by hospitals when its presence is known. Another explanation is that even at this late date in the HIV epidemic, providers in New York State do not recognize that PCP patients demonstrate the most publicized HIV-related opportunistic infection. If so, other, more subtle sequelae of HIV infection maybe being identified at an even lower rate, and treatment of HIVinfected patients may be delayed. Further study of the non-HIV-infected PCP patients would clearly be fruitful. In the absence of such a study, it is prudent to recognize that statewide HIV hospitalization utilization may be underestimated when SPARCS or a comparable system is used as the source. El
:-
In Seattle-King County, the major metropolitan area in Washington State, acquired immunodeficiency syndrome (AIDS) was the third leading cause of death in males aged 25-44years in 1986. In 1987, it was second, according to the King County Department of Vital Statistics. While AIDS continues to increase in importance as a cause of mortality,1 therapeutic advances should eventually be reflected in decreased mortality and longer survival times. Such trends have been reported from major epicenters of the epi-
}>:.-::.:.
demic, such as San Francisco,2 and may be occurring nationwide.3 Our study confirms that survival times of persons living
Address reprint requests to William E. Lafferty, Office of Epidemiology and Surveillance, HIV/AIDS and Infectious Diseases, Washington State Department of Health, 1610 N.E. 150th St., Seattle, WA 98155-7224. Mr. Glidden is with the Biostatistics Department of the University of Washington. Dr. Hopkins is with the Seattle-King County Department of Public Health. This paper, submitted to the Joumal September 26, 1989, was revised and accepted for publication June 21, 1990.
o'
S:::::: SSS::'' ::S}S:
''-
S:::'
SS:::'SS::-' ::SS: :::.S:.::.-
American Journal of Public Health 217
Public Health Bniefs
with AIDS have increased in Washington State independent of changes in the AIDS case definition.
Medtods The Washington State and SeattleKing County human immunodeficiency virus (HIV)-AIDS epidemiology units maintain [a] registry of case reports that meet the Centers for Disease Control (CDC) surveillance definition of AIDS. All resident cases were investigated. Survival analysis was performed only for patients 13 years of age or older that met the pre1987 case definition.4 Cases with more than one primary diagnosis were classified by hierarchy into one of three categories: Pnewnocystis canndi pneumonia (PCP), other diagnosis without PCP, or Kaposi's sarcoma (KS) alone. Passive AIDS case reporting was estimated to be 96 percent and 88 percent complete in 1986 and 1988, respectively, according to methods previously described.5 In December 1988 all presumed surviving cases diagnosed on or before December 1987 were investigated. Provider contact and telephone surveillance are routine and update mortality status yearly. County vital records were reviewed for recent deaths that were either unknown to providers or may not have reached the state's vital records office. County vital records yielded 10 unreported deaths among 286 persons with AIDS who were presumed living after provider contact.
218 American Journal of Public Health
Three cases lost to follow-up were censored at the last date known to be alive. Cohorts were formed of individuals diagnosed in 1985 or before, individuals diagnosed in 1986, and individuals diagnosed in 1987. The groups were compared by means of nonparametric rank tests for censored data6 after adjusting for primary diagnosis but not for any other prognostic variables. The effect of year and diagnosis was also estimated by fitting the Cox proportional hazards model. Hazard comparisons are relative to cases diagnosed before 1986 with KS and were made using BMDP2L.7 Because of the limited amount of data available on any given subject, our ability to investigate and adjust for prognostic variables was limited. The CDC case report forms record the month and year in which an individual is diagnosed and the day, month, and year of death. Approximate survival times were constructed by assuming that all in-
dividuals were diagnosed on the 15th of the month. For the generalized Wilcoxin test this is equivalent to breaking tied death times (tied if counted in months) in favor of individuals who died later in the month. These approximate death times were also used to produce Kaplan-Meier survival curves using PROC Lifetest8 and to produce the relative hazard estimates.
Resuls Through the end of 1987, 777 adult AIDS cases had been reported; 680 met the pre-1987 AIDS case definition. Seventy-one of these cases died within 1 month of diagnosis. Mean age at the time of diagnosis, racial composition, sex, and transmission category of the three temporal cohorts did not change significantly between the intervals (Table 1). Although the proportion of intravenous drug users (IVDUs) increased from 1 percent to 3
February 1991, Vol. 81, No. 2
Public Health Briefs
percent from 1985 to 1987, only 12 IVDUs were included in the study. Overall, the proportion of cases diagnosed as outpatients increased from 11 percent to 20 percent between 1985 and 1987. Of definitively diagnosed cases of KS, 19 percent, 26 percent, and 68 percent were diagnosed as outpatients before 1986, in 1986, and in 1987, respectively (data not shown). Overall, cases survived a median of 14.4 months (Tables 2 and 3). People with KS survived longer than people with PCP. Both groups survived longer than those with other diagnoses. Survival increased in cases diagnosed in more recent years. Cases of PCP and other diagnoses that were diagnosed during 1989 had longer survival times than those diagnosed in 1986 (p < .001, for each comparison). Most people with KS diagnosed in 1987 were still living. Median survival for inpatient cases with primary diagnoses of PCP increased from 12.4, to 15.8, to 20.8 months for the three time intervals, respectively (p < .0001).
Discussion We believe our ascertainment of deaths was fairly complete. Although recent out-of-state deaths could have been missed by these methods, the impact of these cases would be 5 percent or less. In addition, since completion of this study, cases have been matched to the National Death Index. Only two deaths were detected that were not included in this anal-
ysis. Our data confirm that trends seen in
major epicenters of the AIDS epidemic are occurring elsewhere in the United States. Increases in survival for people with primary diagnoses of PCP could be related to PCP prophylaxis and zidovu-
February 1991, Vol. 81, No. 2
dine therapy. Local zidovudine studies treated approximately 52 residents who had PCP diagnosed in 1986. The lack of increase in the median survival of people with other diagnoses from 1985 to 1986 may reflect their ineligibility for zidovudine studies. Although studies in San Francisco have shown a decrease in median survival for people with KS through 1985 and slight increases during 1986 and 1987,2 our KS cohort diagnosed in 1986 survived longer than those diagnosed during or before 1985. The increase in outpatient diagnoses of KS from 1985 to 1987, from 19 percent to 68 percent, suggests this practice may in part be responsible for our local data. The general availability of zidovudine in March 1987 may be responsible in part for the sharp increases in survival seen in 1987. Exclusion of outpatient diagnoses for people with PCP did not reduce median survival; therefore, earlier diagnosis is an unlikely reason for prolonged survival in this cohort. The impact of prolonged survival of people living with AIDS on the health care system needs evaluation. Although CDC case projections for 1990 and beyond have been reduced in cumulative numbers by 16 percent through 1993,9 increased survival may neutralize the effect of fewer new cases on the health care system. Recent federal registration (H.R. 2310) expanding insurance continuation from 18 to 29 months may make health care more accessible to a larger number of people living with AIDS who survive longer than 18 months. However as the use of zidovudine and other antiviral drugs prolongs survival, health care programs need to provide long-term access to people who are otherwise uninsurable. El
Acknowledgments This study was supported by CDC AIDS Surveillance Grant U62/CCU000993-03. The authors thank the AIDS coordinators at the local public health departments for death certificate review and case reporting; Jeanne Honey and Jan Harwell, MPA, MA, for case investigation; Bob Wood, MD, Noreen Harris, DVM, Cathy Critchlow, PhD, Alan Kristal, PhD, and Michael Smyser, MPH, for manuscript review; and Tim Tyree for manuscript preparation. Excerpts from this paper were presented at the 5th International AIDS Conference, June 1989, in Montreal.
References 1. Kristal AR: The impact of the acquired immunodeficiency syndrome virus on patterns of premature death in New York. JAMA 1986; 255:2306-2310. 2. Lemp GF, Payne S, Neal D, et al: Survival trends for patients with AIDS. JAMA 1990;
263:402-406. 3. Harris JE: Improved short-term survival of AIDS patients initially diagnosedwithPneumocystis cainnu pneumonia, 1984 through 1987. JAMA 1990; 263:397-401. 4. Revision of the CDC surveillance case definition for acquired immunodeficiency syndrome. MMWR 1987; 36(suppl. 2s)3-16. 5. Lafferty W, Hopkins S, Honey J, et al: Hospital charges for people with AIDS in Washington State: Utilization of a statewide hospital discharge data base. Am J Public Health 1988; 78:949-952. 6. Cox DR, Oakes D: Analysis of Survival Data. London: Chapman and Hall, 1984. 7. Hopkins A: Survival analysis with covariates: Cox models. In: Dixon WJ, (ed): BMDP Statistical Software. Berkeley: University of California Press, 1985, 576-594. 8. SAS Institute, Inc: SAS User's Guide: Statistics, Version 5 Ed. Cary, NC: SAS Institute, Inc., 1985:529-557, 1989; 111:41-50. 9. Centers for Disease Control: Estimates of HIV prevalence and projected AIDS cases: Summary of a workshop, October 31November 1, 1989. MMWR 39:110-112, 117-119, February 23, 1990.
American Joumal of Public Health 219
