The global burden of typhoid and paratyphoid fevers: a systematic analysis for the Global Burden of Disease Study 2017

BACKGROUND

Efforts to quantify the global burden of enteric fever are valuable for understanding the health lost and the large-scale spatial distribution of the disease. We present the estimates of typhoid and paratyphoid fever burden from the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017, and the approach taken to produce them.

METHODS

For this systematic analysis we broke down the relative contributions of typhoid and paratyphoid fevers by country, year, and age, and analysed trends in incidence and mortality. We modelled the combined incidence of typhoid and paratyphoid fevers and split these total cases proportionally between typhoid and paratyphoid fevers using aetiological proportion models. We estimated deaths using vital registration data for countries with sufficiently high data completeness and using a natural history approach for other locations. We also estimated disability-adjusted life-years (DALYs) for typhoid and paratyphoid fevers.

FINDINGS

Globally, 14·3 million (95% uncertainty interval [UI] 12·5-16·3) cases of typhoid and paratyphoid fevers occurred in 2017, a 44·6% (42·2-47·0) decline from 25·9 million (22·0-29·9) in 1990. Age-standardised incidence rates declined by 54·9% (53·4-56·5), from 439·2 (376·7-507·7) per 100 000 person-years in 1990, to 197·8 (172·0-226·2) per 100 000 person-years in 2017. In 2017, Salmonella enterica serotype Typhi caused 76·3% (71·8-80·5) of cases of enteric fever. We estimated a global case fatality of 0·95% (0·54-1·53) in 2017, with higher case fatality estimates among children and older adults, and among those living in lower-income countries. We therefore estimated 135·9 thousand (76·9-218·9) deaths from typhoid and paratyphoid fever globally in 2017, a 41·0% (33·6-48·3) decline from 230·5 thousand (131·2-372·6) in 1990. Overall, typhoid and paratyphoid fevers were responsible for 9·8 million (5·6-15·8) DALYs in 2017, down 43·0% (35·5-50·6) from 17·2 million (9·9-27·8) DALYs in 1990.

INTERPRETATION

Despite notable progress, typhoid and paratyphoid fevers remain major causes of disability and death, with billions of people likely to be exposed to the pathogens. Although improvements in water and sanitation remain essential, increased vaccine use (including with typhoid conjugate vaccines that are effective in infants and young children and protective for longer periods) and improved data and surveillance to inform vaccine rollout are likely to drive the greatest improvements in the global burden of the disease.

FUNDING

Bill & Melinda Gates Foundation.

Enteric fever in young Yoruba children

Ninety-seven Nigerian children under 5 years of age had typhoid or paratyphoid fever proved by blood culture. The presented with fever, anaemia, gastrointestinal or neurological disturbances, and typhoid and paratyphoid appeared clinically indistinguishible. In this holoendemic malarial area, malaria was the most important differential diagnosis, and may have contributed to the concomitant anaemia seen in the majority of patients. Despite vigorous therapy with chloramphenicol or trimethoxazole, and blood transfusion where indicated, the mortality in both typhoid and paratyphoid was high (18% in both groups).

Interaction of aflatoxin and paratyphoid infections in broiler chickens

There was a significant (P less than 0.05) interaction resulting in increased mortality in chickens fed aflatoxin and infected with Salmonella worthington, S. thompson, S. derby, or S. typhimurium var. copenhagen which cause paratyphoid. There was no interaction on body weight or spleen weight; however, there wan an interaction with all four Salmonella species resulting in enlarged livers from which Salmonella could be isolated with increased frequency. Aflatoxin caused a decrease in total serum proteins but a dramatic increase in anti-Salmonella agglutinins in infected birds. These results suggest that aflatoxin impairs some component of the immune system other than that forming humoral antibodies and perhaps other than the reticuloendothelial system which have been reported previously to be impaired during aflatoxicosis in the chicken.

Case Fatality Rate of Enteric Fever in Endemic Countries: A Systematic Review and Meta-analysis

Enteric fever is a febrile illness, occurring mostly in Asia and Africa, which can present as a severe and possibly fatal disease. Currently, a case fatality rate (CFR) of 1% is assumed when evaluating the global burden of enteric fever. Until now, no meta-analysis has been conducted to summarize mortality from enteric fever. Therefore, we conducted a systematic review and meta-analysis to aggregate all available evidence. We estimated an overall CFR of 2.49% (95% confidence interval, 1.65%-3.75%; n = 44), and a CFR in hospitalized patients of 4.45% (2.85%-6.88%; n = 21 of 44). There was considerably heterogeneity in estimates of the CFR from individual studies. Neither age nor antimicrobial resistance were significant prognostic factors, but limited data were available for these analyses. The combined estimate of the CFR for enteric fever is higher than previously estimated, and the evaluation of prognostic factors, including antimicrobial resistance, urgently requires more data.

Changes in the pattern of mortality following the eradication of hyperendemic malaria from a highly susceptible community

The population of the sugar estates of the Guyana coastlands was 110 000 in 1966; malaria was eradicated between 1945 and 1951. A study has been made of the pattern of mortality before and after malaria eradication, during the 30-year period from 1937 to 1966.The decline in general mortality has greatly exceeded the fall in mortality specifically related to malaria and has continued for almost 10 years after registration of the last death from malaria. In infants, mortality has been reduced, mainly through a decline in the number of deaths from prematurity and congenital debility that were due mainly to malaria and its sequelae in the expectant mother. In children (1-14 years of age) the decline has resulted from the disappearance of malaria and chronic nephritis as causes of death. In adults, mortality has fallen mainly through the progressive decline in the incidence of a number of diseases not overtly related to malaria: acute and chronic respiratory diseases, chronic nephritis, and the anaemias. Cardiovascular diseases, on the contrary, have shown a tendency to increase since malaria was brought under control.