Schwarcz et al. Respond to "Should We Estimate Incidence for Undefined Populations?"

Sandra Schwarcz, William McFarland, Mitchell Katz and Hillard Weinstock

1 San Francisco Department of Public Health, San Francisco, CA.
2 Centers for Disease Control and Prevention, Atlanta, GA.

Abbreviations: HIV, human immunodeficiency virus; STD, sexually transmitted disease


    INTRODUCTION
 TOP
 INTRODUCTION
 REFERENCES
 
Schoenbach et al. (1Go) question our analysis of human immunodeficiency virus (HIV) incidence among patients attending a sexually transmitted disease (STD) clinic (2Go). They state that the incidence estimates we provided are difficult to interpret because they are not derived from a stable base population. Additionally, they note that incidence rates found in this setting cannot be directly generalized to a larger population. As they correctly explain, seeking care at a STD clinic is a function of a number of probabilities, including risk, infection, perceptions, and health access issues.

We fully agree with Schoenbach et al. that our incidence rates cannot be applied directly to other populations. The same could be said for virtually any longitudinal cohort study of HIV incidence. For example, what is the base population of the convenience sample of homosexual men that comprises the Multicenter AIDS Cohort Study (3Go, 4Go) or the STD clinic-recruited sample of homosexual men in the City Clinic cohort (5Go, 6Go)? Although the base populations that these cohorts represent are difficult to define and results from such studies cannot easily be generalized, the incidence findings from these cohorts have provided valuable information. Application of the Serologic Testing Algorithm for Recent HIV Seroconversion strategy can be used to estimate incidence from anonymous, unlinked cross-sectional surveys, thereby eliminating selection and withdrawal biases that may occur with longitudinal studies.

While it is difficult to know precisely how findings from STD clinic patients may be generalized to the entire population, these patients have been a well-studied and characterized population over many years (7Go, 8Go). Patterns and changes in risk behaviors and levels of HIV infection in STD clinic patients may present before they are noticeable in the general population. It is for this reason that the Centers for Disease Control and Prevention selected STD clinics as HIV sentinel surveillance sites (9Go). Monitoring these high-risk populations can provide meaningful information with which to direct prevention interventions. That is, after all, one of the most important outcomes of public health surveillance activities.


    NOTES
 
Reprint requests to Dr. Sandra Schwarcz, AIDS Surveillance, San Francisco Department of Public Health, 25 Van Ness Avenue, Suite 500, San Francisco, CA 94102.


    REFERENCES
 TOP
 INTRODUCTION
 REFERENCES
 

  1. Schoenbach VJ, Poole C, Miller WC. Should we estimate incidence for undefined populations? Am J Epidemiol 2001;153:935–7.[Free Full Text]
  2. Schwarcz, S, Kellogg T, McFarland W, et al. Differences in the temporal trends of HIV seroincidence and seroprevalence among sexually transmitted disease clinic patients, 1989–1998: application of the Serologic Testing Algorithm for Recent HIV Seroconversion. Am J Epidemiol 2001;153:925–34.[Abstract/Free Full Text]
  3. Kingsley LA, Zhou SY, Bacellar H, et al. Temporal trends in human immunodeficiency virus type 1 seroconversion 1984–1989. A report from the Multicenter AIDS Cohort Study (MACS). Am J Epidemiol 1991;134:331–9.[Abstract]
  4. Polk BF, Fox R, Brookmeyer R, et al. Predictors of the acquired immunodeficiency syndrome developing in a cohort of seropositive homosexuals, methods, and uses of sentinel surveillance for HIV in the United States. Public Health Rep 1990;105:113–19.[ISI]
  5. Rutherford GW, Lifson AR, Hessol HA, et al. Course of HIV-1 infection in a cohort of homosexual and bisexual men: an 11 year follow-up study. BMJ 1990;301:1183–8.[ISI][Medline]
  6. Francis DP, Hadler SG, Thompson SE, et al. The prevention of hepatitis B with vaccine: report of the Centers for Disease Control multi-center efficacy trial among homosexual men. Ann Intern Med 1982;97:362–6.[ISI][Medline]
  7. Schwarcz SK, Kellogg TA, Kohn RP, et al. Temporal trends in human immunodeficiency virus seroprevalence and risk behavior at the San Francisco municipal sexually transmitted disease clinic, 1989–1992. Am J Epidemiol 1995;142:314–22.[Abstract]
  8. Weinstock HS, Sidhu J, Gwinn M, et al. Trends in HIV seroprevalence among persons attending sexually transmitted disease clinics in the United States, 1988–1992. J Acquir Immune Defic Syndr Hum Retrovirol 1995;9:514–22.[ISI][Medline]
  9. Pappaioanou M, Sonsweo TJ Jr, Petersen LR, et al The family of HIV seroprevalence surveys: objectives, methods, and uses of sentinel surveillance for HIV in the United States. Public Health Rep 1990;105:113–19.[ISI]
Received for publication January 23, 2001. Accepted for publication January 30, 2001.


Related articles in Am. J. Epidemiol.:

Differences in the Temporal Trends of HIV Seroincidence and Seroprevalence among Sexually Transmitted Disease Clinic Patients, 1989–1998: Application of the Serologic Testing Algorithm for Recent HIV Seroconversion
Sandra Schwarcz, Timothy Kellogg, William McFarland, Brian Louie, Robert Kohn, Michael Busch, Mitchell Katz, Gail Bolan, Jeff Klausner, and Hillard Weinstock
Am. J. Epidemiol. 2001 153: 925-934. [Abstract] [FREE Full Text]  

Invited Commentary: Should We Estimate Incidence for Undefined Populations?
Victor J. Schoenbach, Charles Poole, and William C. Miller
Am. J. Epidemiol. 2001 153: 935-937. [Extract] [FREE Full Text]  




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