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Influence of study population on the identification of risk factors
for sexually transmitted diseases using a case-control design: the example
of gonorrhea.
American Journal of Epidemiology 2004;160(4):393-402.
Manhart LE, Aral SO, Holmes KK, Critchlow CW, Hughes JP, Whittington WLH,
Foxman B.
Abstract
The population prevalence of many sexually transmitted diseases (STDs) is low.
Thus, most epidemiologic studies of STDs are conducted among STD clinic populations
to maximize efficiency. However, STD clinic patients have unique sociobehavioral
characteristics. To examine the potential effect of study population on identification
of risk factors, the authors compared 1) STD clinic patients with a random
digit dialing telephone sample, 2) general population cases with random digit
dialing controls, and 3) STD clinic cases with STD clinic controls (Seattle,
Washington, 1992-1995). Risk factors for gonorrhea identified among STD clinic
patients formed a subset of those identified in the general population. In
both populations, risk decreased with age (odds ratio for the general population
(OR(GP)) = 0.4, 95% confidence interval (CI): 0.22, 0.59; odds ratio for
the clinic population (OR(clinic)) = 0.5, 95% CI: 0.30, 0.81) and was increased
among Blacks (OR(GP) = 15.5, 95% CI: 4.93, 49.0; OR(clinic) = 10.5, 95% CI:
4.51, 24.68) and persons whose partner had been jailed (OR(GP) = 5.4, 95%
CI: 2.07, 13.9; OR(clinic )= 3.1, 95% CI: 1.32, 7.30). Additional factors
associated with gonorrhea in the general population included secondary education
(OR = 0.3, 95% CI: 0.11, 0.70), anal intercourse (OR = 10.5, 95% CI: 2.01,
54.7, STD history (OR = 5.9, 95% CI: 1.76, 19.5), meeting partners in structured
settings (OR = 0.2, 95% CI: 0.09, 0.50), no condom use (OR = 3.2, 95% CI:
1.30, 7.89), and divorce (OR = 3.6, 95% CI: 1.07, 11.9). Risk factors identified
in STD clinics will probably be confirmed in a general population sample,
despite overcontrolling for shared behaviors; however, factors associated
with both disease and STD clinic attendance may be missed.
