Abstracts: ISEE 20th Annual Conference, Pasadena, California, October 12–16, 2008: Contributed Abstracts
Proper understanding of seasonality of enteric infections will improve our knowledge of host-pathogen biology and enhance our capability to predict future outbreaks. Rotavirus and cryptosporidiosis have distinct seasonal patterns depending on geographic location. Rotavirus shows distinct peaks during cooler months in temperate climate but no such seasonality is observed in tropical climates. On the other hand, cases of cryptosporidiosis tend to increase during warm rainy season in the tropics, whereas it peaks during winter and fall in temperate zones. This study assessed seasonality of childhood diarrhea in general, and diarrhea due to rotavirus and Cryptosporidium spp. in particular.
Materials and Methods:
We conducted a weekly time-series analysis of data available from a birth cohort study in Vellore, South India. A total of 452 children were recruited at birth and followed up for three years on a twice-weekly basis. Fecal samples were collected from all children fortnightly as part of routine surveillance. Additionally, fecal samples were collected from any child who developed diarrhea, identified either by a routine field worker visit or self-referral by the mother. Data on all diarrheal episodes experienced by the cohort were extracted and merged with the database containing stool microbiology results. For rotavirus, only those samples positive by RT-PCR was considered positive. Cryptosporidium spp. was identified by microscopy of stool samples. Staggering recruitment was adjusted for by assessing seasonality of prevalence rates per 1000 child weeks. Seasonality was assessed for all diarrheal episodes as well as for the rotavirus and cryptosporidial diarrhea separately. Linear and quadratic trend were adjusted to account for potential changes in symptomatology due to protective immunity associated with re-exposure in the aging cohort.
The cohort experienced a total of 2005 episodes of diarrhea, out of which 289 were due to rotavirus and 57 due to Cryptosporidium spp. Diarrhea overall peaked in the first week of June (week 24). In the last week of August in the second and fourth year of follow-up peaks of diarrhea due to Cryptosporidium spp. were detected. Rate of rotavirus diarrhea peaked in second week of October (week 42) and had high amplitude in the first year that diminished over time. G1 and G2 were the most common genotypes for rotavirus whereas C. hominis was the most common species of Cryptosporidium identified. Strain-specific analysis showed both G1 and G2 rotavirus to have a well-defined seasonality with a significant negative trend. G1 appeared to exhibit a biannual peak with high intensity, whereas G2 strain appeared in an annual basis with less intensity. Coinciding peaks of G1 and G2 amplified the overall rotavirus intensity.
This study uses data from a community-based diarrheal disease study to look at the seasonality of diarrhea overall, and rotavirus and cryptosporidial diarrhea in children in south India. Preliminary findings suggest a strong seasonal pattern in potentially waterborne infection that was pronounced during hot and dry season. Further analysis will control for meteorological parameters including temperature and precipitation, behavioral factors, and water quality.