Part I. Analysis of data gaps pertaining to Salmonella enterica serotype Typhi infections in low and medium human development index countries, 1984-2005

Abstract

There are only 10 contemporary, population-based studies of typhoid fever that evaluate disease incidence using blood culture for confirmation of cases. Reported incidence ranged from 13 to 976/100 000 persons per year. These studies are likely to have been done preferentially in high- incidence sites which makes generalization of data difficult. Only five of these studies reported mortality. Of these the median (range) mortality was 0% (0-1.8%). Since study conditions usually involved enhanced clinical management of patients and the studies were not designed to evaluate mortality as an outcome, their usefulness for generalizing case-fatality rates is uncertain. No contemporary population-based studies reported rates of complications. Hospital-based typhoid fever studies reported median (range) complication rates of 2.8% (0.6-4.9%) for intestinal perforation and case-fatality rates of 2.0% (0-14.8%). Rates of complications other than intestinal perforation were not reported in contemporary hospital-based studies. Hospital-based studies capture information on the most severe illnesses among persons who have access to health-care services limiting their generalizability. Only two studies have informed the current understanding of typhoid fever age distribution curves. Extrapolation from population-based studies suggests that most typhoid fever occurs among young children in Asia. To reduce gaps in the current understanding of typhoid fever incidence, complications, and case-fatality rate, large population-based studies using blood culture confirmation of cases are needed in representative sites, especially in low and medium human development index countries outside Asia.

Fig. 1

Geographic distribution of population-based studies of typhoid fever incidence. (Adapted from Crump et al. [1].) ■, High incidence (>100 episodes/100 000 per year); , Medium incidence (10–100 episodes/100 000 per year); , Low incidence (<10 episodes/100 000 per year); □, region with human development index (HDI) countries; ○, site of contributing disease incidence study.

Fig. 2

Age-specific incidence of typhoid fever (from Crump et al. [1]). —, High (>100/100 000 per year); – – –, medium (10–100/100 000 per year); - - - -, Low (<10/100 000 per year).

Fig. 3

Incidence of typhoid fever by per capita gross domestic product (adjusted for purchasing power) of low- and medium-HDI countries, 1984–2005 (n=10 studies).