Variation of genotype and prevalence of Noro virus in U.S. students in Mexico with Traveler\u27s Diarrhea, summer of 2004 and 2005

Noro virus, a positive single stranded RNA virus has been identified as a major etiologic agent in food borne gastroenteritis and diarrheal diseases. The emergence of this organism as a major non-bacterial cause in such outbreaks is partly due to the improved diagnostic tools like Reverse Transcription Polymerase chain reaction (RTPCR) that enable its detection. Noro virus accounts for nearly 96% of non-bacterial gastroenteritis outbreaks in US (1). Travelers\u27 Diarrhea (TD) has remained a constant public health risk in the developed nations for decades and bacteria like Entero toxigenic Escherichia coli, Entero aggregative Escherichia coli have been described as the main etiologic agents for TD (2-4). A possible viral contribution to TD has been discovered in two studies (5, 6). The current study was designed to determine the prevalence of Noro virus in a population of 107 US students with TD acquired in Mexico in 2005 and to compare the prevalence to the prevalence of Noro virus in a similar study done in 2004. This study involved the testing of clinical stool specimens from 107 subjects in 2005 for the presence of Noro virus using RTPCR. The prevalence of Noro virus in 2004 used for comparison to 2005 data was obtained from published data (5). All subjects were recruited as TD subjects in a randomized, double-blinded clinical trial comparing a standard three day dosing of Rifaximin with and without an anti motility drug Loperamide. The prevalence of Noro virus geno group I was similar in both years, but geno group II prevalence differed across the two years (p = 0.003). This study finding suggests that the prevalence of Noro virus geno groups varies with time even within a specific geographic location. This study emphasizes the need for further systematic epidemiologic studies to determine the molecular epidemiology and the prevalence patterns of different geno groups of this virus. These are essential to planning and implementation of public health measures to lessen the burden of TD due to Noro virus infection among US travelers.