Abstract
BackgroundIn surveillance for typhoid fever, under-detection of cases occurs when patients with fever do not seek medical care, or seek medical care but do not receive a blood test. Missing data may result in incorrect estimates of disease incidence.MethodsWe used data from an ongoing randomised clinical trial of typhoid conjugate vaccine among children in Nepal to determine if eligible patients attending our fever clinics who did not have blood taken for culture had a lower risk of disease than those who had blood drawn. We assessed clinical and demographic predictors of having blood taken for culture, and predictors of culture-positive results. Missing blood culture data were imputed using multiple imputations.ResultsDuring the first year of surveillance, 2392 fever presentations were recorded and 1615 (68%) of these had blood cultures. Children were more likely to have blood taken for culture if they were older, had fever for longer, a current temperature ≥38 degrees, or if typhoid or a urinary tract infection were suspected. Based on imputation models, those with blood cultures were 1.87 times more likely to have blood culture-positive fever than those with missing data.ConclusionClinical opinion on the cause of the fever may play a large part in the decision to offer blood culture, regardless of study protocol. Crude typhoid incidence estimates should be adjusted for the proportion of cases that go undetected due to missing blood cultures while adjusting for the lower likelihood of culture-positivity in the group with missing data.
Highlights
Typhoid and paratyphoid fever are enteric infections caused by the bacteria Salmonella enterica serovars Typhi
Clinical opinion on the cause of the fever may play a large part in the decision to offer blood culture, regardless of study protocol
We aimed to determine whether those who did not have a blood culture were different in terms of clinical and demographic characteristics to those who did have blood taken for culture and, whether they were more or less likely to test blood culture positive for typhoid fever
Summary
Typhoid and paratyphoid fever are enteric infections caused by the bacteria Salmonella enterica serovars Typhi [1] Blood culture surveillance programmes are essential for understanding which countries have a high burden of disease. Surveillance programmes aim to estimate the incidence of disease by detecting all cases of blood culture-positive typhoid fever in a given population or at sentinel surveillance sites, but the quality of surveillance can vary substantially between countries.[2] If under-detection of cases occurs, disease incidence will be under-estimated. Missed cases can occur when patients with fever do not seek medical care, attend a clinic that is not part of the study surveillance programme, or seek medical care but do not receive a blood culture test required for diagnosis. In surveillance for typhoid fever, under-detection of cases occurs when patients with fever do not seek medical care, or seek medical care but do not receive a blood test. Missing data may result in incorrect estimates of disease incidence
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