Enteric fever is common in tropical regions and is caused by Salmonella enterica serotype typhi (S typhi ). For diagnosis of enteric fever, the Widal test is the most widely used test after blood culture. In HIV infected individuals false positive and false negative Widal reactions are common. The result is variable titres and baseline titres that are unusual in this patient population.
This study was done to determine the baseline antibody titres for S typhi among HIV infected individuals.
Average baseline antibody titres against O and H antigens of S typhi were measured by standard Widal test in 200 HIV positive asymptomatic individuals, as well as 200 age and sex-matched controls. The results were compiled and statistically analysed.
A total of 84 (42%) of the cases had an H antibody titre of >1:20 and 105 (52.5%) had a titre of >1:20 against O antigen. This implies that positive titre of H and O antigen is significantly associated with HIV positive cases with P<0.001. Correlation of CD4 count with antibody titres shows that there is no significant association between CD4 counts and antibody titres against either H (P=0.634) or O antigen (P=0.765)
This study shows that HIV infected individuals had increased titres of antibodies against S typhi from the baseline. This indicates a need for evaluation of current cut-off values of diagnostic titres for this group. We also suggest that it is best to perform baseline titres against S t yphi for each patient at the time of diagnosis of HIV status, and to use this for future reference.