Sep 19, 2012

Noroviruses Affecting Diverse Populations Dr. Hoonmo L. Koo

SAN FRANCISCO – As the availability of more sensitive diagnostic methods such as reverse transcription-polymerase chain reaction testing become more widespread, noroviruses are increasingly being recognized as important enteric pathogens in diverse populations.

"In the past, much of our knowledge about noroviruses has been hindered because we don’t have a good animal model or method for culturing norovirus," Dr. Hoonmo L. Koo said at the annual Interscience Conference on Antimicrobial Agents and Chemotherapy. "The majority of our current understanding has come from studying human outbreaks, volunteer challenge studies, and evaluating surrogate caliciviruses such as feline and murine caliciviruses, which don’t cause human infection but can be cultured."
Courtesy CDC/Charles D. Humphrey

"Each year, noroviruses [pictured] cause about 21 million cases of infection in the United States."

Noroviruses (NoVs) are classified into five genetic groups based on their RNA capsid sequences, with genogroup I (GI) and genogroup II (GII) NoVs causing the most human NoV infections. GII.4 NoV strains are the predominant circulating genotype in the United States and worldwide, said Dr. Koo of Baylor College of Medicine, Houston. As reverse transcription-polymerase chain reaction testing (RT-PCR) has become more available in recent years, NoVs "are now recognized as the most definable common cause of acute nonbacterial gastroenteritis worldwide," he said. "They account for approximately half of all food-borne illness in the United States.
"Each year, NoVs cause about 21 million cases of infection in the United States. They occur throughout the year, but they peak in the winter season."
NoV outbreaks are common in children, travelers, restaurant patrons, military personnel, patients, and health care staff at hospitals, nursing homes, and other medical facilities. Dr. Koo and his associates conducted an 8.5-year surveillance study at Texas Children’s Hospital (TCH) investigating NoV, rotavirus (RV), and adenovirus prevalence at the facility before and after introduction of the RV vaccine in 2006. The study evaluated 8,173 stool samples from inpatients and outpatients at TCH from February 2002 to June 2010. The samples were evaluated for RV by antigen detection or electron microscopy and adenoviruses by electron microscopy. In addition, a subset of 3,222 stools were evaluated for NoV by RT-PCR (J. Ped. Infect. Dis. 2012 Aug. 3 [doi:10.1093/jpids/pis070]).
"We found that RV prevalence decreased significantly after the introduction of the RV vaccine in 2006,"
 Dr. Koo said at the meeting, which was sponsored by the American Society for Microbiology. "In more recent years, it decreased from about 9% in 2007 to 3% in 2010." At the same time, he continued, "NoV prevalence increased in 2004 and was consistently between 11% and 17% from 2004 to 2010. There was no significant increase in NoV prevalence after the RV vaccine was introduced in 2006."
The researchers concluded that NoVs have emerged as the most common viral gastroenteritis pathogen at TCH, which is one of the largest pediatric hospitals in the United States. "We believe that as RV prevalence continues to decline with vaccination, NoVs will soon eclipse rotaviruses as the most important cause of pediatric gastroenteritis in the United States and other countries where the RV vaccine is successfully administered," Dr. Koo said. Continue 

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