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7.4. Screening and/or mass-treatment
Since 1992 the prevalence of syphilis in pregnant women has been monitored in Nairobi. The
seroprevalence rate of syphilis among pregnant women in Nairobi has decreased
significantly in recent years. From a seroprevalence of 7.2% in 1994, over 7.3% in 1995, to
4.5% in 1996, 3.8% in 1997, we showed a syphilis serology among pregnant women of 3.0%
in 1998, and this both at the antenatal clinics and at the maternity hospital (Jenniskens
1995). Compared to the early years of the decentralized program, the quality of the syphilis
control program has improved considerably. For instance, partner referral and treatment at
antenatal clinics was 50% in 1992-93 and was as high as 75% in 1997-1998. However,
partner referral at postpartum reached only 36%, indicating that the well being of the unborn
child is an important determinant in partner notification. We showed in another study that
antenatal treatment of RPR positive women significantly improved pregnancy outcome but
the risk of adverse outcome remained 2.5-fold higher than the risk observed in uninfected
mothers (Temmerman 2000). Adverse pregnancy outcome was also related to lack of
partner treatment during pregnancy (Gichangi 2000). Presumptive STI treatment during
pregnancy resulted in reduced rates of STI as well as in improved neonatal outcome
(Gichangi 1997, Gray 2001).
However, we also showed that routine syphilis screening in this low seroprevalence rate
situation, is expensive and its effectiveness doubtful. Indeed, the proportion of patients with a
positive test result who actually have the disorder (PPV) is directly related to the prevalence
of the disease within the population for any given sensitivity and specificity of a diagnostic
test. This means that for a given test, the lower the prevalence of the disorder in a population
the greater the number of false positives. On the extreme, as the prevalence of a disease in
a population approaches zero, the PPV of any diagnostic test also approaches zero, a
concept depicted graphically by Ryan et al. (1998).
Under certain circumstances, mass treatment of a selected population group within a
community or region can be contemplated, for instance in situations where prevalence rates
of STIs are high and where laboratory facilities are insufficient or absent or when dealing with
highly mobile populations (WHO 1986). Prevalence rates can be reduced rapidly with mass
treatment, but in many if not all instances some infected individuals within the community and
region are not treated, and reintroduction of infection from outside the community or region
remains likely. Modeling indicates that STI prevalence would, after substantial reduction,
return to baseline levels over 5-10 years (Korenromp 2000). High rates of re-infection as can
be expected for instance in sex workers would necessitate periodic treatment supplemented
CONCLUSIONS 105