Evaluation of an Electricity-free, Culture-based Approach for Detecting Typhoidal Salmonella Bacteremia during Enteric Fever in a High Burden, Resource-limited Setting

Background: In many rural areas at risk for enteric fever, there are few data on Salmonella enterica serotypes Typhi (S. Typhi) and Paratyphi (S. Paratyphi) incidence, due to limited laboratory capacity for microbiologic culture. Here, we describe an approach that permits recovery of the causative agents of enteric fever in such settings. This approach involves the use of an electricity-free incubator based upon use of phase-change materials. We compared this against conventional blood culture for detection of typhoidal Salmonella. Methodology/Principal Findings: Three hundred and four patients with undifferentiated fever attending the outpatient and emergency departments of a public hospital in the Kathmandu Valley of Nepal were recruited. Conventional blood culture was compared against an electricity-free culture approach. Blood from 66 (21.7%) patients tested positive for a Gram-negative bacterium by at least one of the two methods. Sixty-five (21.4%) patients tested blood culture positive for S. Typhi (30; 9.9%) or S. Paratyphi A (35; 11.5%). From the 65 individuals with culture-confirmed enteric fever, 55 (84.6%) were identified by the conventional blood culture and 60 (92.3%) were identified by the experimental method. Median time-to-positivity was 2 days for both procedures. The experimental approach was falsely positive due to probable skin contaminants in 2 of 239 individuals (0.8%). The percentages of positive and negative agreement for diagnosis of enteric fever were 90.9% (95% CI: 80.0%–97.0%) and 96.0% (92.7%–98.1%), respectively. After initial incubation, Salmonella isolates could be readily recovered from blood culture bottles maintained at room temperature for six months. Conclusions/Significance: A simple culture approach based upon a phase-change incubator can be used to isolate agents of enteric fever. This approach could be used as a surveillance tool to assess incidence and drug resistance of the etiologic agents of enteric fever in settings without reliable local access to electricity or local diagnostic microbiology laboratories.Boston Children's Hospital (Frederick H. Lovejoy Fund)Harvard Global Health InstituteNational Institute of Allergy and Infectious Diseases (U.S.) (Grant AI100023)National Institute of Allergy and Infectious Diseases (U.S.) (Grant AI077883

Bacteria isolated among participants in the study according to culture method (either, conventional, or experimental).

<p>Bacteria isolated among participants in the study according to culture method (either, conventional, or experimental).</p

Sample temperature readings from phase-change incubator.

<p>Example of temperature readings, recorded every five minutes inside the incubator over a period of 72 hours. Exchange of phase change packets was performed daily (red arrows) to “recharge” the incubator and leads to brief periods of lower temperatures followed by higher temperatures (inset), which were not found to impact bacterial growth.</p

Culture-confirmed diagnosis of enteric fever by conventional blood culture in comparison with results from the experimental procedure.

*<p>The experimental blood culture was positive in two additional patients that were negative by conventional blood culture, but the organisms were probable skin contaminants. These are captured in percent agreement calculations.</p

Flow diagram of patients recruited and enrolled in the study.

<p>Flow diagram of patients recruited and enrolled in the study.</p