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Original Papers
Gastrointestinal infection and food poisoning
INTRODUCTION
Norovirus (NoV) has historically been designated 'winter vomiting diseases', later as 'Norwalk virus' and 'Norwalk-like virus', and finally as 'norovirus' [1, 2]. NoV can be classified into five genogroups (GI-GV) by phylogenic analysis of the capsid protein. Human NoV infections are caused by GI, GII, and, to a lesser extent, GIV [3]. Genogroups GI and GII of human NoV are further classified into 14 and 17 subgenotypes, respectively [4]. Symptoms of NoV include acute-onset vomiting, watery diarrhoea, and nausea. Healthy adults usually recover without complications [5]. NoV can be transmitted efficiently due to the low infectious dose and the high viral load in faeces and vomitus [6].
Historically, NoV outbreaks were under-reported; however, with development of reverse transcription-polymerase chain reaction (RT-PCR)-based diagnostics, NoV has been recognized as a leading cause of gastroenteritis worldwide [7]. Over-reporting of disease is also possible due to a lack of proof that NoV detected by PCR is viable, and able to cause illness or be transmitted. In the USA, NoV is the most common cause of foodborne illness outbreaks. The primary mode of transmission is person-to-person, followed by foodborne, environmental contamination, and waterborne transmission [8]. As many as 19-21 million NoV cases, including 56 000-71 000 hospitalizations, and 570-800 deaths, are reported annually in the USA [9].
Outbreaks of gastroenteritis (defined as [= or >, slanted]2 cases of a similar illness) in South Korea are reported to the Korea Centers for Disease Control and Prevention (KCDC), and NoV was designated in South Korea as a national notifiable infectious disease in 2006. During 2007-2009, NoV was the most common pathogen identified in foodborne disease outbreaks, occurring most frequently from November to May [10].
In February 2012, a NoV outbreak in elementary school A was reported. In succession, another NoV outbreak occurred in elementary school B, about 20 km from school A. We conducted epidemiological investigations to characterize the extent of the outbreaks, identify the mode of transmission, and determine the relationship between the outbreaks.
METHODS
The outbreaks
On 4 February 2012, a school nurse from school A reported to a local health authority that more than 20 students had diarrhoea or vomiting. On 15 February, a local...