Clinic- vs. Population-Based Studies of STD Lisa E. Manhart 1, Sevgi O. Aral 2, King K. Holmes 1, Cathy W. Critchlow 1, James P. Hughes 1, William L. H. Whittington 1, Betsy Foxman 3 University of Washington, Seattle, WA 1 ; Centers for Disease Control, Atlanta, GA 2 University of Michigan, Ann Arbor, MI 3

Population Levels General population STD Clinic population

Background Population prevalence relatively low (CDC, 2001; NCHS)Population prevalence relatively low (CDC, 2001; NCHS) Study populations drawn from STD clinicsStudy populations drawn from STD clinics

Sociobehavioral Risk Factors Sexual activity level discordance (Garnett, 1996) Concurrent sex partners (Potterat, 1999) Race/age discordance (Aral, 1999) Non-white race (CDC, 2001) Low SES (Barnes, 1984) Young age at sexual debut (Aral, 1999) Unprotected intercourse (Aral, 1999) Multiple partners (Seidman, 1988) Douching (Scholes, 1993) Young age at sexual debut (Aral, 1999) Unprotected intercourse (Aral, 1999) Multiple partners (Seidman, 1988) Douching (Scholes, 1993)

Sources of risk factor data STD clinic studiesSTD clinic studies Population based surveysPopulation based surveys –NHANES- NSAM –NSFG- NATSAL –Add Health- DHS Limited comparisons (Garnett, STD 1996; Johnson, STI 2002)Limited comparisons (Garnett, STD 1996; Johnson, STI 2002) –Lifetime number partners –Concurrent partners –Condom use patterns

Methods Cross-sectional: Compare STD clinic population to RDD population Compare STD clinic population to RDD populationCase-control: a)General population case-control study to identify risk factors for gonorrhea b)STD clinic case-control study to identify risk factors for gonorrhea

Cross-sectional analysis STD Clinic ( ) 373 Seattle STD clinic attendees Age years Seeking care for STD symptoms or contact to STD Behavioral interview, including most recent partner in past 90 days STD Clinic ( ) 373 Seattle STD clinic attendees Age years Seeking care for STD symptoms or contact to STD Behavioral interview, including most recent partner in past 90 days RDD Survey (1995) 376 Seattle residents Age years Random-digit-dial (RDD) telephone sample Behavioral interview, including most recent partner in past 90 days RDD Survey (1995) 376 Seattle residents Age years Random-digit-dial (RDD) telephone sample Behavioral interview, including most recent partner in past 90 days

Cross-sectional comparison* * p<0.05 for all comparisons

Sexual Behavior & Partnership Characteristics* (cross-sectional) * p<0.05 for all comparisons

Case-control studies Risk factors for gonorrhea STD clinic* CASESCONTROLS CASESCONTROLS N=61 N=332 N=61 N=332 GC diagnoses Attendees GC diagnoses Attendees w/o GC w/o GC Behavioral Behavioral Behavioral Behavioral survey survey survey survey * unweighted logistic regression STD clinic* CASESCONTROLS CASESCONTROLS N=61 N=332 N=61 N=332 GC diagnoses Attendees GC diagnoses Attendees w/o GC w/o GC Behavioral Behavioral Behavioral Behavioral survey survey survey survey * unweighted logistic regression General population* CASESCONTROLS CASESCONTROLS N=103 N=376 N=103 N=376 41% from NRL † RDD resp. 41% from NRL † RDD resp. 59% from clinic 59% from clinic Behavioral Behavioral Behavioral Behavioral survey survey survey survey * weighted logistic regression performed to account for unequal distribution of source of cases † Neisseria Reference Laboratory General population* CASESCONTROLS CASESCONTROLS N=103 N=376 N=103 N=376 41% from NRL † RDD resp. 41% from NRL † RDD resp. 59% from clinic 59% from clinic Behavioral Behavioral Behavioral Behavioral survey survey survey survey * weighted logistic regression performed to account for unequal distribution of source of cases † Neisseria Reference Laboratory

Factors associated with gonorrhea among heterosexuals (age 18-39) General population STD Clinic population Age ( per 5 yrs) Black Hx STD Never use condoms Income $9375-$17,499 ≥HS Income >17,500 Income not reported Jail Anal sex Divorced Structured mtg. Odds ratio (log scale)

Limitations Participation bias in RDD?Participation bias in RDD? RF may be specific to SeattleRF may be specific to Seattle Restricted age range [18-39]Restricted age range [18-39] No laboratory ascertainment of disease in RDD control groupNo laboratory ascertainment of disease in RDD control group

Conclusions RF in STD clinic are likely to be confirmed in general populationRF in STD clinic are likely to be confirmed in general population STD clinic studies may miss some RF identified in general populationSTD clinic studies may miss some RF identified in general population Base choice of study population on:Base choice of study population on: –Question of interest –Available resources

Template for OR plot General Population

Template for OR plot STD Clinic Pop

Factors associated with gonorrhea among year-old heterosexuals General populationSTD Clinic population Age Black Hx STD Never use condoms Income $9375-$17,499 ≥HS Income >17,500 Income not reported Jail Anal sex Divorced Structured mtg Odds ratio (log scale)

STD Clinic 403 enrolled RDD Survey 544 enrolled RDD Survey 544 enrolled p-ship >90 days 22 out of age range 33 not sexually active 30 same-sex partner 8 same-sex partner

Guidelines for study population selection High prevalence No stigma General population Low prevalence Stigma Clinic-based population