Typhoid fever in children: some epidemiological considerations from Karachi, Pakistan

The morbidity of typhoid fever is highest in Asia with 93% of global episodes occurring in this region. Southeast Asia has an estimated incidence of 110 cases/100,000 population, which is the third highest incidence rate for any region. Pakistan falls into this region. There is also a considerable seasonal variation of typhoid fever, carrying significant public health importance. Children are worst affected. Population-based data from Pakistan are scarce.

From June 1999 to December 2001 a fortnightly surveillance system was established in two squatter settlements in Karachi, Pakistan, with two study centers, each staffed by a doctor and five community health workers. Cases of continuous high-grade fever for three or more days were referred to these centers and screened clinically. Blood culture and Typhidot tests were done.

One-third of the 4198 cases with febrile episodes of three or more days detected in the community were screened at the centers; 341 were clinically suspected of having typhoid fever. Forty-nine were positive by culture whereas 161 were positive by serology. Ten cases were multi-drug resistant. Incidence of culture-proven typhoid was estimated to be 170 (95% CI: 120, 220)/100,000 population, whereas serology-based incidence was 710 (95% CI: 620, 810)/100,000 population. Peak incidence was noted in October followed by May and June.

Passive surveillance, even when augmented by household visits, misses a significant portion of suspected cases. Morbidity of typhoid is quite high in Pakistan and needs public health intervention. Hot months have higher incidence of typhoid. Healthcare behavior studies will help to develop a better surveillance system.