A Massey University study, recently published in the New Zealand Medical Journal, looked at 175 gastroenteritis outbreaks reported to a North Island public health provider over a five-year period by rest homes, early childhood centres (ECE), hospitals and a defence facility.

The study found a trend of increased notifications of  institutional vomiting and diarrhoea outbreaks – mostly caused by norovirus – over the five years (between 2009-2014). As well as a link between reporting an outbreak early and a reduction in the number of people affected and how long the outbreak lingered.

The 175 gastro outbreaks involved more than 4500 people – often the very elderly or the very young ­– with most of the institutional outbreaks being reported by aged care facilities (98 outbreaks from 31 facilities), followed by ECE (50 outbreaks from 23 centres) and the remaining outbreaks from hospitals (26 outbreaks from three hospitals) and a defence facility (1). More than half of the total 57 facilities reporting outbreaks had more than one outbreak with the most outbreaks per facility (21) being reported by a hospital.

A third of the outbreaks (64) were notified quickly to public health within one day after the onset of symptoms of the second case; while at the other end of the spectrum 20 per cent (36) were not notified for a week or more. The researchers found that the shorter the notification time the shorter the duration and smaller impact of the gastro outbreak – even after adjusting for type of facility and gastro bug.

“The act of notification to public health services (PHS) per se will help reduce the impact of the outbreaks more effectively if the facility’s procedures for controlling outbreaks have oversight by a regulatory authority,” say the researchers. “If a facility notifies early then the PHS is able to provide earlier access to advice and action that support the facility’s procedures for controlling outbreaks, including support with implementing the Ministry of Health (MoH) Norovirus guidelines.”

The research found no statistical evidence of a seasonal pattern but did find a trend for more outbreaks in the spring and autumn. It also found a significant increased trend in the number of notified outbreaks over the five-year period, which reflected a national trend and one also seen in an US study of hospital outbreaks.

“The increased ageing population (accompanied by a presumed rise in the number of people in residential aged care), the funded 20 hours ECE, the introduction of national guidelines of norovirus management in hospital and aged care on 2 January 2009 and the emergence of the virulent Sydney GII.4 strain of norovirus could have contributed to this increasing trend,” said the researchers.

Norovirus was the most commonly identified pathogen causing the gastroenteritis outbreaks (108), followed by rotavirus (14) and sapovirus (9). Other pathogens, i.e. Clostridium difficile, Campylobacter spp. and Cryptosporidium spp., were identified in three outbreaks. The pathogen was unidentified in 41 outbreaks.

Norovirus is the most common cause of epidemic non-bacterial gastroenteritis worldwide and in New Zealand it has been the most common cause of  institutional gastroenteritis outbreaks since 2007.

Food-borne or person-to-person contamination is the most common cause of norovirus outbreaks. The overall attack rate in New Zealand outbreaks is about 40–60 per cent of the people exposed to the virus, but the researchers report that it can be even higher in institutional outbreaks.

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