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Weekly Report Detail

19 September 2017

General bacterial and protozoal outbreaks of infectious intestinal disease reported to HPS in 2016

ObSurv is the surveillance system established in 1996 for all general outbreaks of infectious intestinal disease (ID) in Scotland. For the purpose of ObSurv an outbreak is defined as an incident in which two or more linked cses experience the same illness or when the observed number of cases unaccountably exceeds the expected number. The system seeks information on general outbreaks, defined as outbreaks affecting members of more tan one household or residents of an institution.

Bacterial outbreaks

During 2016, five general outbreaks of shigatoxigenic Escherichia coli (STEC) were reported, all five being ientified as serogroup O157. Two of these were Phage Type 21/28 and there was one each of Phage Type 54, Phage Type 28 and Phage Type 8. The five general outbreaks reported in 2016 is comparable with previous yars with four in 2015, and an average of seven STEC outbreaks per annum over the preceding 10 years (2006-2015).

In three of the outbreaks the main mode of transmission was considered to be foodborne, in one environmental and not known in one. The largest of the outbreaks reported in 2016 was an outbreak of E. coli O157 associated with unpasteurised cheese (more information available at http://www.hps.scot.nhs.uk/pubs/detail.aspx?id=3200).

The laboratory-confirmed cases in the general outbreaks accounted for 21% of the total number of reports of E. coli O157 in Scotland during 2016 (see full STEC report for 2016 at http://www.hps.scot.nhs.uk/ewr/redirect.aspx?id=75299) showing that the majority of cases are either sporadic or single household clusters.

There were two general outbreaks of Salmonella reported in 2016, which is slightly lower than in previous years with five in 2015, three in both 2013 and 2014, and an average of four per year over the preceding ten years (2006-2015). Both the outbreaks in 2016 were of S. Enteritidis and in both the suspected vehicle of transmission was eggs. Both these Salmonella outbreaks were part of larger European outbreak. More information is available at https://ecdc.europa.eu/en/news-events/epidemiological-update-multi-country-outbreak-salmonella-enteritidis-phage-type-8-mlva and https://ecdc.europa.eu/en/publications-data/rapid-risk-assessment-multi-country-outbreak-salmonella-enteritidis-phage-types.

Although Campylobacter is the most common bacterial cause of infectious intestinal disease, most cases are apparently sporadic, and no general outbreaks were identified in 2016. This is in line with the trend seen in recent years with one Campylobacter outbreak in both 2012 and 2014, and none in either 2013 or 2015.

Protozoal outbreaks

Four general outbreaks of Cryptosporidium were reported in 2016, compared to three in 2015 and a ten-year average (2006-2015) of two per annum. With such small numbers, however, random year-on-year variation can be expected. The mode of transmission in two of the outbreaks was waterborne, one was person to person, and one was environmental.

No general outbreaks of Giardia were reported in 2016. General outbreaks of Giardia are relatively unusual in Scotland, with two general Giardia outbreaks reported in the preceding 10 years, one each in 2009 and 2015.

Toxin mediated outbreaks

There were no toxin mediated outbreaks caused by Staphylococcus aureus, Bacillus cereus, Clostridium perfringens or scombrotoxin in 2016.

HPS would like to thank all the consultants in public health medicine, health protection nurses, infection control nurses, environmental health officers and microbiologists who contribute to the outbreak surveillance system.

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Author(s): Prepared by: GIZ team Vol: 51 No: 37 Year: 2017 Page: