We were able to determine the laboratory-confirmed incidence of these 2 infections over 2 separate time periods, which allowed us to identify both the incidence and the proportion of incident laboratory-confirmed infections that were asymptomatic. We also were able to determine the proportion of those uninfected or treated at baseline and 12 months who subsequently became reinfected with either organism. The high incidence of C. trachomatis infection confirmed the need for more aggressive routine screening and treatment of STIs in these populations. A public health strategy would need to include methods that encouraged asymptomatic individuals who engage in risky behaviors to seek screening for STIs. The relatively low incidence of N. gonorrhoeae limited our ability to evaluate predictors of asymptomatic infections with this organism, but the comparable incidence between the baseline and 12 month assessments and between 12 and 24 months visits suggest the need for enhanced efforts to control the spread of this organism as well.
The high proportion of participants (16.4%) reinfected with either C. trachomatis
or N. gonorrhoeae
within 1 year confirms the observation by others that there are core transmitters of STIs who are part of high-prevalence pools.1
STI control efforts should identify these core transmitters for more intensive interventions including contact tracing, partner notification, and treatment.
The high proportion of participants infected with either C. trachomatis
or N. gonorrhoeae
with no reported symptoms is particularly disturbing as it complicates identification and treatment of infected individuals. Individuals who have no symptoms are unlikely to seek testing and treatment unless they are motivated by public health messages, community health educators, or health care providers. The higher proportion of asymptomatic C. trachomatis
infection and asymptomatic gonorrhea in men has been previously reported.18–20
Potterat et al estimated that approximately 35% of gonorrhea transmitted from men is from those who are asymptomatic,21
and Wiesner and Thompson estimated that 60% to 80% of transmission of gonorrhea was from asymptomatic men.22
While upper-income countries have implemented programs to identify and treat asymptomatic infections with screening programs, in low-income countries, the proportion of those with asymptomatic infection who may transmit infection to others needs to be evaluated, and the cost-effectiveness of interventions to control them needs to be assessed.
Multivariate analysis for the predictors of these infections underscores the need to focus on women, those with multiple partners, and younger age groups for intervention efforts, as well as on high-risk men reporting no symptoms. Women are vulnerable to infection through their male partners, and youth are likely to experiment with sex in the absence of knowledge and trust their partners; thus, they are unlikely to use condoms.23
Clearly, age-appropriate education about safer sexual methods and symptomatic and asymptomatic STIs needs to be implemented before initiation of sexual activity which often begins shortly after puberty.
The apparently disparate results of the multivariate analysis indicating an association with multiple partners with incident infection but with fewer partners among those with incident infection who report no symptoms suggests that the likelihood of symptomatic infection is associated with intensity of exposure. This is reinforced by the considerably higher proportion of women in India who were sex workers (who have many more partners than those engaging in casual sex) who report symptoms, compared to the other study areas where few of the participants identified themselves as sex workers. However, this observation could also reflect a greater likelihood that sex workers are more aware of the symptoms of sexually transmitted diseases and more likely to report them. Since the sex workers in India were not establishment-based, however, it is unlikely that they received preemptive treatment.
The quality of the laboratory findings of these 2 infections is likely to be very accurate (i.e., it is unlikely that false positives or negatives substantially affected the study results).24
The laboratories in the 5 countries were rigorously standardized and an ongoing quality control program was in place including retesting of a sample of positive and negative specimens and blind testing of standard specimens at the Johns Hopkins Reference Laboratory.16,17,25
Although this was not a clinic-based study, the particular groups selected in each country were selected on the likelihood that many in their group engaged in sex with multiple partners. Thus, these results may be most applicable to the riskier populations in these countries. Another consideration is the impact of spontaneous cure of C. trachomatis
infection in the absence of treatment, which has been reported in 18% to 44% of infected individuals and increases with time since diagnosis.26–29
Thus, we may have missed some incident infections, including those that were treated in the 12-month intervals between the surveys, which would have affected the numerator for determining both incidence and the proportion of symptomatic incident infections.30
The comparability of the proportion of prevalent asymptomatic infections and incident asymptomatic infections, however, suggests that incident infection only modestly overestimates the proportion who are asymptomatic, especially for C. trachomatis
infections, assuming that the cross-sectional data from the 3 surveys reflect the proportion of asymptomatic infections occurring during the 2 incident intervals.
Generalization of the findings across different populations in 5 countries should be done with caution. However, the high proportion of asymptomatic infections across all 5 countries among both men and women suggests that high levels of asymptomatic infections occur in most populations and settings.
In conclusion, this study reinforces the need to implement more aggressive public health programs to identify, treat, and control STIs in these countries, and underscores the need to target women, younger persons, those with multiple partners, and “core transmitters.” The study also reveals the urgent need to determine the extent to which infected individuals without symptoms in low- and middle-income countries can transmit their infections to others and the benefits of screening programs of high-risk populations.