Pathogen-Specific Burden of Outpatient Diarrhea in Infants in Nepal: A Multisite Prospective Case-Control Study

Abstract

Background: Nonsevere diarrheal disease in Nepal represents a large burden of illness. Identification of the specific disease-causing pathogens will help target the appropriate control measures.

Methods: Infants aged 6 weeks to 12 months were recruited from 5 health facilities in eastern, central, and western Nepal between August 2012 and August 2013. The diarrhea arm included infants with mild or moderate diarrhea treatable in an outpatient setting; the nondiarrhea arm included healthy infants who presented for immunization visits or had a mild nondiarrheal illness. Stool samples were tested for 15 pathogens with a multiplex polymerase chain reaction (PCR) assay and real-time reverse-transcription (RT)-PCR assays for rotavirus and norovirus. Rotavirus- and norovirus-positive specimens were genotyped. We calculated attributable fractions (AFs) to estimate the pathogen-specific burden of diarrhea and adjusted for facility, age, stunting, wasting, and presence of other pathogens.

Results: We tested 307 diarrheal and 358 nondiarrheal specimens. Pathogens were detected more commonly in diarrheal specimens (164 of 307 [53.4%]) than in nondiarrheal specimens (113 of 358 [31.6%]) (P < .001). Rotavirus (AF, 23.9% [95% confidence interval (CI), 14.9%-32.8%]), Salmonella (AF, 12.4% [95% CI, 6.6%-17.8%]), and Campylobacter (AF, 5.6% [95% CI, 1.3%-9.8%]) contributed most to the burden of disease. In these diarrheal specimens, the most common genotypes for rotavirus were G12P[6] (27 of 82 [32.9%]) and G1P[8] (16 of 82 [19.5%]) and for norovirus were GII.4 Sydney (9 of 26 [34.6%]) and GII.7 (5 of 26 [19.2%]).

Conclusions: The results of this study indicate that the introduction of a rotavirus vaccine in Nepal will likely decrease outpatient diarrheal disease burden in infants younger than 1 year, but interventions to detect and target other pathogens, such as Salmonella and Campylobacter spp, should also be considered.

Keywords: Campylobacter; Nepal; Salmonella; diarrhea; norovirus; rotavirus.

Figure 1.

Percentages of infections in the diarrhea (A) and nondiarrhea (B) arms, according to pathogen and age group. The numerator is number of persons in that age group whose sample tested positive for a specific infection; the denominator is number of persons in the age group. Abbreviations: Adeno, adenovirus; C.diff, Clostridium difficile; E.coli, Escherichia coli; ETEC, enterotoxigenic Ecoli LT/ST; Norovirus, Norovirus GI/GII; STEC, Shiga-like toxin producing E coli stx₁/stx₂.

Figure 2.

Infections and cumulative enrollment in the diarrhea arm, according to month of the year (September 2012 through August 2013). The numerator is number of persons in that month whose sample tested positive for a specific infection; denominator is the number of persons enrolled in that month. Abbreviations: C. difficile, Clostridium difficile; E. coli, Escherichia coli LT/ST; ETEC, enterotoxigenic E cofi; Norovirus, Norovirus GI/GII; STEC, Shiga-Toxin producing E coli stx₁/stx₂; V. cholerae, Vibrio cholerae.