On October 18, 2011, the Southern Nevada Health District (SNHD), Office of Epidemiology received reports of gastrointestinal illness from two independent groups of patrons of Restaurant A located in Las Vegas. People from both groups ate during dinner hours at the restaurant on October 14, 2011. Of the eight people from the two groups, seven reported symptoms of diarrhea and/or vomiting after they consumed food from Restaurant A.

In response to these illness reports, the SNHD initiated an investigation. symptoms, and identical norovirus (NoV) genetic sequences were detected from ill persons of two independent dining parties. No ill person was hospitalized, and no death occurred.

NoV can spread via direct contact with NoV‐containing fecal matter or aerosolized vomitus, or by indirect contact with them via environmental surfaces. The high propensity of NoV for person‐to‐person spread might explain illnesses among primary‐cases and their household contacts. The outbreak appeared to have been confined to Restaurant A and did not spread to the general community.

Ice water and margaritas were significantly more likely to be consumed among primary cases when compared to controls diners, and were consumed by nearly all primary‐case diners.

Drinking water or ice contaminated with NoV has resulted in outbreaks in food‐service settings. However, the contamination of frequently served food items such as water and ice (also a main ingredient for margarita) in a high‐volume restaurant would have resulted in numerous diners becoming ill, and cannot explain the relatively small number of diners who complained of illness after eating at Restaurant A on and after October 14. An alternative explanation may be that infected staff member(s) might have contaminated the food prior to serving them to customers.

The low inoculums (≥18 viral particles) required for transmission of NoV, and prolonged period of fecal shedding of the virus can enable infected food handlers to contaminate food products . Additionally, the majority of interviewed staff at Restaurant A admitted to pouring and serving drinks, and frequently placing garnishes (e.g. lemons, limes, and other fruits) into beverages prior to serving them to customers. Coupled with EH observations that employees handled ready‐to‐eat food using bare hands, the contamination of beverages with NoV could have occurred via infected worker(s) using bare hands to dispense or garnish beverages. Minimizing bare hand contact with ready‐to‐eat food is recommended as a mean of interrupting disease transmission. Workers whose job duties include preparing food and beverages must minimize bare hand contact with ready‐to‐eat food, including items used as garnishes for food and drinks.

Abstract below:
We describe an investigation of an outbreak of norovirus infection at a restaurant in Las Vegas, Nevada that was suspected to be associated with restaurant staff using bare hands to place garnishes into beverages. We conducted a case‐control study and surveillance for additional illnesses, performed inspections of the restaurant, and collected stool specimens to test for norovirus. Eight ill restaurant patrons and 23 control subjects were interviewed.
Univariate analysis showed several food items were associated with illness, but only ice water and margarita were consumed by members of all affected dining groups. Four stool specimens were positive for norovirus by real‐time reverse transcriptase‐polymerase chain reaction, with all four sequenced specimens being identical and closely related to norovirus strain GII.4J Apeldorn NLD07. To prevent such outbreaks, restaurant workers whose job duties include
preparing food and beverages must minimize bare hand contact with ready‐to‐eat food, including items used as garnishes for food and drinks.

On Nov. 13, 2009, a Belgian physician notified authorities about an apparent cluster of Shigella sonnei; ultimately, 52 cases were identified over two months, and most were linked to a canteen in a public institution building. Best guess is that a food handler who travelled to Morocco shortly before detection of the first laboratory-confirmed case, picked up shigella, and then transmitted it through food.

The details can be found in the current issue of Epidemiology and Infection, where researchers report on a matched case-control study to test an association between shigellosis and canteen-food consumption.

The three food handlers working permanently in the canteen responded to the questionnaire. Food handler A travelled to Turkey from 23 September to
4 October 2009. She started working on 7 October. She prepared sandwiches, washed dishes and served food. She fell ill on 20 October, and had been exposed to canteen food during the 4 days prior to disease onset. Food handler B travelled to Morocco from 23 September to 1 October. This person started working on 4 October and was involved in vegetable washing, preparation of hot meals, sandwiches, cold dishes involving vegetables and cleaning the canteen. He did not declare having fallen sick. Food handler C was also involved in all activities except in hot meal preparation. He had not travelled, been absent or fallen sick.

Of the 52 shigella cases found in 708 employees of a public institution in Flemish Brabant province, Belgium, between September and November 2009, seven cases were confirmed as S. sonnei. There was a common PFGE profile which resembled those from archived specimens from Morocco. Cases of
shigellosis were associated with canteen-food consumption.

Investigators worked with three hypotheses: (i) waterborne transmission through a contaminated water dispenser, (ii) person-to-person transmission or via surfaces (toilets), or (iii) foodborne transmission (through previously contaminated food or during the preparation process by a contaminated food handler).

Foodborne transmission through canteen food is supported by the results of the employee survey and by the matched case-control study. This led us to think that a food handler might have been the source of the outbreak. Food handler B returned from Morocco shortly before the appearance of the first confirmed cases. He did not report any symptoms and worked continuously since his return.

Foodborne transmission might have happened had he been an asymptomatic case. Healthy carriers can shed 102 Shigella c.f.u./g of feces during 1 month.
Thus, food handler B could have unintentionally acted as an intermittent source of food contamination during the period of faecal shedding. Conversely, food handler A, who had travelled to Turkey, could not be the source of the outbreak, since her onset of disease happened after the onset of symptoms of some confirmed cases.

The researchers recommend:
• washing hands with soap and water before eating and after defecation for employees and food handlers;
• preventing sick food handlers from working until full recovery or until negative fecal culture in the case of laboratory confirmation;
• maintaining surveillance of further possible cases of shigellosis through the institution’s prevention service; and,
• collecting information on the workplace when interviewing notifiable cases in order to detect infectious disease clusters early.

Shigellosis outbreak linked to canteen-food consumption in a public institution: a matched case-control study
01.feb.11
Epidemiology and Infection
I. Gutiérrez Garitano, M. Naranjo, A. Forier, R. Hendriks, K. De Schrijver, S. Bertrand, K. Dierick, E. Robesyn, and S. Quoilin
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=8024291
Abstract
On 13 November 2009, the authorities of Flemish Brabant, Belgium, received an alert concerning a potential outbreak of Shigella sonnei at a public institution. A study was conducted to assess the extent, discover the source and to implement further measures. We performed a matched case-control study to test an association between shigellosis and canteen-food consumption. Water samples and food handlers' faecal samples were tested. The reference laboratory characterized the retrospectively collected Shigella specimens. We found 52 cases distributed over space (25/35 departments) and time (2 months). We found a matched odds ratio of 3·84 (95% confidence interval 1·02–14·44) for canteen-food consumption. A food handler had travelled to Morocco shortly before detection of the first laboratory-confirmed case. Water samples and food handlers' faecal samples tested negative for Shigella. Confirmed cases presented PFGE profiles, highly similar to archived isolates from Morocco. Foodborne transmission associated with the canteen was strongly suspected.