Abstract:

Background: Failure or inappropriate diagnosis of enteric fever remains a challenge in Tanzania, and most often results into the over - prescription of antibiotics to febrile patients suspected of enteric fever. This in turn can potentially result into morbidity, mortality, and the escalation of the burden of antimicrobial resistance and healthcare costs. Evaluation of the utility of the Widal test in Tanzania has revealed contradicting results (especially in studies where antibody titration was not done). Recently, several point-of-care Salmonella spp. antigen tests have been developed. However, the utilities of these tests have not been evaluated in the northwestern part of Tanzania.

Objectives: To determine the utility of the rapid immunochromatographic test and the Widal test versus blood culture as a gold standard to diagnose enteric fever among febrile patients with gastrointestinal symptoms attending outpatient services at Sengerema District Designated Hospital (SDDH), Mwanza - Tanzania.

Methodology: This was a cross-sectional analytical study conducted at SDDH from December 2018 to March 2019 involving febrile out-patients. Data was collected using a pre-tested interviewer administered questionnaire. Slide and tube agglutination Widal tests (using VoXbank kits manufactured by Voxtur Bio Ltd®, in India) for the determination of antibody titer and a pointof-care rapid Salmonella typhi and Salmonella paratyphi antigen test were done using Laborex test kits®, manufactured by Zhejiang Orient Gene Biotech Co. Ltd® in China. Furthermore, blood culture was performed to isolate bacterial pathogens (including Salmonella spp.) causing febrile illness and their antimicrobial susceptibility patterns to guide specific patients’ management. Data analysis was performed using STATA version 13.0 software

Results: The overall prevalence of blood stream infections was 19.9% (65/327), with predominance of infections due to Escherichia coli (49.2%, n=32) and Salmonella spp. (35.4%, n=23). The prevalence of Salmonella-attributable blood stream infection was 7.0% (23/327) and that with enteric fever was 5.2 % (17/327). The proportions of Typhoidal-blood stream infections were 26.2% (17/65) and for non-Typhoidal-blood stream infections were 9.2% (6/65). HIV seropositivity was significantly associated with a higher risk of Salmonella-attributable blood stream infections [OR (95% CI): 5.92 (1.62 - 21.63), p=0.007)]. The sensitivity and specificity of Widal test were 88.2% and 88.7%, respectively. On the other hand, the sensitivity and specificity of the rapid immune chromatographic test were 29.4% and 100%, respectively. Antimicrobial sensitivities of S. typhi and S. paratyphiA were as follows: piperacillin-tazobactam (58.8%), gentamicin (23.5%), ciprofloxacillin (88.2%), and ceftriaxone (82.4%). The prevalence of extended spectrum beta lactamases production (ESBL) among Gram negative bacteria was 8.6% (5/58); the ESBL producers were Klebsiella pneumoniae (n=2); Salmonella typhimurim (n=2) and Salmonella typhi (n=1).

Conclusion: The prevalence of Salmonella-attributable blood stream infections was low (7.0%). The rapid immunochromatographic test had low sensitivity (29.4%) but very high specificity (100%) in diagnosing enteric fever. The antimicrobial sensitivity profiles to most antimicrobial agents in this rural setting remain promising with only 8.6% of bacteria being ESBL producers. The Widal test may have a role if Salmonella anti-O and H titrations are properly done. There is an urgent need to evaluate alternative rapid antigen-based immunochromatographic tests with high sensitivities.