# Presentation: 100760

## Clinic- vs. Population-Based Studies of STD

- Lisa E. Manhart1, Sevgi O. Aral2, King K. Holmes1, Cathy W. Critchlow1,
- James P. Hughes1, William L. H. Whittington1, Betsy Foxman3
*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)
- Study 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)

## Sources of risk factor data

- STD clinic studies
- Population based surveys
- NHANES		- NSAM
- NSFG		- NATSAL
- Add Health		- DHS
- 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
**Case-control:**
- General population case-control study to identify risk factors for gonorrhea
- STD clinic case-control study to identify risk factors for gonorrhea

## Cross-sectional analysis

- STD Clinic (1992-1995)
- 373 Seattle STD clinic attendees
- Age 18-39 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 18-39 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*
-  **CASES****	****CONTROLS**
-    N=61	  N=332
-    GC diagnoses	  Attendees
- 	    w/o GC
-    Behavioral 	  Behavioral
-      survey	    survey
- * unweighted logistic regression

- General population*
-  **CASES**	**CONTROLS**
-    N=103	  N=376
-    41% from NRL†	  RDD resp.
-    59% from clinic
-    Behavioral 	  Behavioral
- 	   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**

- Odds ratio (log scale)

- Odds ratio (log scale)

## Limitations

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

## Conclusions

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

## Slide 14

## Template for OR plotGeneral Population

## Template for OR plotSTD Clinic Pop

## Factors associated with gonorrhea among 18-39 year-old heterosexuals

- General population

- STD Clinic population

- Odds ratio (log scale)

- Odds ratio (log scale)

**STD Clinic**
**403**** enrolled**

**RDD Survey**
**544**** enrolled**

- 381

**373**

- 439

- 406

**376**

**105** 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