The systematic review yielded 24 studies that examined typhoid fever incidence and employed blood culture as the criteria for diagnosis () [11
]. Five advanced surveillance systems reporting blood-culture confirmed typhoid fever cases were also identified [35
]. In addition, after the manuscript was accepted, we became aware of one recently published study that met systematic review inclusion criteria, so the analysis was updated to include this data [40
]. In total, typhoid fever incidence data was abstracted from 47 countries across 14 (67%) of the 21 regions (). Population-based and prospective vaccine studies contributed data for 13 countries across 8 regions. The remaining incidence data was collected by typhoid fever surveillance systems in the 6 developed regions, each of which includes 1 or more countries with national-level surveillance. The developed regions include: High Income Asia Pacific, High Income North America, Central Europe, Eastern Europe, Western Europe, and Australia/New Zealand. Overall, our analysis includes national-level incidence data from 34 countries across these regions. Paratyphoid fever incidence data was available for 9 countries representing 7 (33%) of the 21 regions (). Only 2 regions included national-level surveillance systems reporting paratyphoid fever incidence (High Income Asia Pacific and Australia/New Zealand). Population-based studies provided paratyphoid fever data for 7 countries in 5 of the regions (Southern Latin America, North Africa/Middle East, South Asia, South East Asia, and East Asia). The median year of data collection for included studies is 2004.
Selection strategy flow diagram used to identify studies on typhoid and paratyphoid fever.
Input data for typhoid fever incidence rates and summarized median incidence rates by Super Region*
Input data for paratyphoid fever incidence rates and summarized median incidence and mortality rates by Super Region*
Input data for typhoid and paratyphoid fever were grouped into 7 Super Regions and median incidence rates and interquartile ranges are presented in and , respectively. Paratyphoid fever incidence estimates were extrapolated between Super Regions on the basis of typhoid fever burden estimates. No paratyphoid fever data were available for Super Region 2 (Central Europe, Eastern Europe, Central Asia), Super Region 3 (Southern Sub-Saharan Africa, Central Sub-Saharan Africa, West Sub-Saharan Africa, East Sub-Saharan Africa), and Super Region 7 (Caribbean, Andean Latin America, Central Latin America, Tropical Latin America, Oceania). Extrapolations were made from Super Region 1 (Australia/New Zealand, Southern Latin America, High Income North America, High Income Asia Pacific, Western Europe) to Super Region 2; Super Region 5 (South Asia) to Super Region 3; and Super Region 6 (East Asia and South East Asia) to Super Region 7.
Twenty-two (88%) of the 25 eligible typhoid fever incidence studies contained age-specific typhoid fever data for children <5 years and persons ≥5 and older (). Age-specific data were available for 6 (29%) of 21 regions representing 5 of 7 Super Regions. All data came from low- and middle-income countries. The median proportion of typhoid fever episodes among children <5 years was 57.7%, and among persons ≥5 years, 42.3%. For Super Regions 3 and 5, the median proportion of typhoid fever cases among each age strata was used to calculate regional estimates of annual number of cases and incidence rates for each age group ().
An overview of studies with age-specific typhoid fever incidence rates by Super Regions
Annual number of typhoid fever episodes, 2010 by Super Region*
The median typhoid fever incidence rate for each Super Region applied to the 2010 population estimates generates a crude global estimate of 13474369 typhoid fever episodes each year (). After adjusting for the low sensitivity of the blood culture typhoid test we estimate typhoid fever incidence to be 26948739 episodes annually.
There is little data to describe typhoid or paratyphoid fever case-fatality rates. In the most recent study on the global typhoid fever burden, Crump et al. assumed a case-fatality rate of 1% for typhoid fever based on hospital-based data, expert opinion, and mortality rates documented by advanced national surveillance systems [1
]. Given we found no new data to suggest an improvement in typhoid fever case fatality rates, we also used this figure to estimate the total number of annual deaths and to derive mortality estimates, which are presented in . Past studies on the global paratyphoid fever burden have not reported mortality estimates. Our study assumed a case-fatality rate of 0.5% given that paratyphoid fever is generally less severe than typhoid fever [42
]. Mortality estimates for paratyphoid fever are presented in .
Summarized median typhoid fever mortality rates by Super Region*