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Indiana State Department of Health

Epidemiology Resource Center Home > Surveillance and Investigation > Surveillance and Investigation Division > Newsletters > Indiana Epidemiology Archived Newsletters > Outbreak Spotlight Outbreak of Viral Gastroenteritis Among Attendees of Two Recreational Vehicle Trade Shows



Outbreak Spotlight is a regularly occurring feature in the Indiana Epidemiology Newsletter to illustrate the importance of various aspects of an outbreak investigation.

Mona Wenger, MPH

ISDH Field Epidemiologist, District 2

 

Kelly Jollif

Epidemiologist/Emergency Preparedness Supervisor, St. Joseph County Health Department

 

Background

On March 14, 2008, the Indiana State Department of Health (ISDH) and the St. Joseph County Health Department (SJCHD) were notified of a gastroenteritis outbreak at two recreational vehicle trade shows.  Over 238 individuals from 30 states, Puerto Rico, and 5 providences in Canada attended the shows. Eleven different meals were prepared and served at two adjoining facilities (one meal was served at an off-site location). In addition, the attendees consumed meals at various other restaurants, and the two groups arrived on different dates.  Symptoms reported included vomiting and diarrhea.

Epidemiologic Investigation
The SJCHD and the ISDH initiated a collaborative investigation and conducted two cohort studies. A complete list of attendees and their contact information was obtained from the organizers of the two trade shows. The menus for the meals served were obtained from the two adjoining facilities. Notification and subsequent updates were sent to all involved states via CDC’s Epi-X system and the National Foodborne Outbreak Listserv.  The ISDH contacted public health officials in Puerto Rico and Canada via telephone.

Table 1: Trade Show One Meal Service and Dates

 

March 9

March 10

March 11

March 12

March 13

Facility A

Dinner

Dinner

Dinner

Dinner

0

Facility B

0

Lunch

Lunch

Lunch

Lunch

Table 2: Trade Show Two Meal Service and Dates

 

March 11

March 12

Facility A

0

0

Facility B

Lunch and Dinner

Lunch (off site)

Questionnaires were developed to determine illness onset, symptom history, and food consumption.  Public health officials in Indiana, multiple states, Canada, and Puerto Rico conducted 119 case interviews.  A case was defined as any previously healthy person who attended either trade show from March 9-14, 2008, or who was a contact of a trade show attendee and developed diarrhea or vomiting after March 9. The illness onset dates ranged from March 12-16 (Figure 1). The attack rate for Trade Show One was 12.5 percent, and the attack rate for Trade Show Two was 65.0 percent.  Predominant symptoms included diarrhea (92.5%) and vomiting (77.5%). Twelve cases consulted health care providers, and one case was hospitalized.  Forty-six individuals met the case definition. Secondary cases were noted during the investigation.

Figure 1: Epidemiologic Curve and Arrival Dates for Both Trade Shows

 

The following events were analyzed to evaluate the significance of association between illness and specific trade show events: 1) contact with ill people, 2) eating at other restaurants, and 3) eating any of the 11 trade show meals. Only two events, both associated with Trade Show One, were found to be statistically significant.
Table 3 shows the p-values for the meals and all trade show attendees.

Table 3: Significant Events

 

Adjusted Risk Ratio (95% CI)

P-Value

March 12 Lunch

17.57 (1.19 – 260.00)

0.037

March 12 Dinner

12.05 (1.98 – 73.19)

0.007

Figure 2: Epidemiologic Curve and Facility B Meals Served to Both Groups

Environmental Assessment

The SJCHD Food Protection Division inspected the two facilities where food was prepared and served.  The inspection revealed that potatoes were not being properly washed prior to utilizing for potato soup in Facility B. The potato soup was served to both groups on separate days and had been cooled in one large container rather than separated into shallow pans as per food regulations. Although five employees from the facility were reported ill, none of the five was a food handler.

The SJCHD did not inspect Facility A because no ill employees were identified, and only participants from Trade Show One had consumed meals there.

Laboratory Results

The ISDH and SJCHD collected three stool samples and submitted them to the ISDH Laboratory for analysis. All three samples tested positive for Norovirus. The Arizona State Health Department and the City of Houston Health Department each reported one positive Norovirus specimen. The five positive Norovirus results included three attendees from Trade Show One, one attendee from Trade Show Two, and one employee from Facility B.  Given the positive Norovirus results, no bacterial testing was performed.

Conclusions

The investigation confirmed that an outbreak of Norovirus did occur during the recreational vehicle trade shows.  Illness was not identified in any other groups. The epidemiologic curve illustrates that the outbreak began during Trade Show Two, one day after participants arrived and within the typical incubation period for Norovirus, and included at least one Facility B employee (Figure 1). Both groups were provided lunch at Facility B on March 11-12, allowing for person-to-person and fomite transmission among the attendees and possible transmission by Facility B employees (Figure 2). The employees and attendees also shared the same restroom facilities.

No events were found to be statistically significant for Trade Show Two. There were two events statistically associated with illness during Trade Show One (Table 3). Those from Trade Show One who attended the lunch at Facility B on March 12 were more likely to become ill than those who did not attend (Table 3).  This was the second meal that was served in Facility Two for the two groups (Figure 2).  Those from Trade Show One who attended the dinner at Facility A on March 12 were more likely to become ill than those who did not attend (Table 3). This event took place during the first illness onset during Trade Show One and contributed to transmission by person-to-person contact (Figure 2).

No food items were significant in the analysis. The findings from the food inspection warranted corrective actions, but they were not contributing factors to the outbreak.

Viral gastroenteritis is passed in the stool or vomit of infected people (fecal-oral route). The virus is easily spread by contaminated food or beverages, from person to person, and by contact with a contaminated object. These viruses can remain infectious on surfaces for up to 72 hours, and only a very small amount of virus is needed to cause infection.

Symptoms include watery diarrhea, vomiting, nausea, cramps, headache, muscle aches, and tiredness. Symptoms usually begin 24-48 hours (range: 12-72 hours) after exposure and last 24-48 hours. The illness can last 72-84 hours in the elderly or in those with weakened immune systems. Most cases have no, or slight, fever. Infected people can shed the virus for as long as two weeks after recovery.

Recommendations

In general, most Norovirus outbreaks can be prevented by strictly adhering to the following guidelines:

·            Practice good hygiene:

·         Thoroughly wash hands with soap and water after using the restroom; after changing diapers; after assisting someone with diarrhea and/or vomiting; after swimming; and before, during, and after food preparation.

·         Clean food preparation work surfaces, equipment, and utensils with soap and water before, during, and after food preparation.

·            Eat safe foods and drink safe water (Remember: Contaminated foods may look and smell normal.):

·         Wash all produce before eating raw or cooking.

·         Use treated water for washing, cooking, and drinking.

·            Protect others:

·         Persons with diarrhea and/or vomiting should not prepare food or provide health care for others and should limit direct contact with others as much as possible.

·         Persons with diarrhea and/or vomiting should not attend a child-care facility or school.

·         Persons with diarrhea and/or vomiting shall be excluded from employment involving food handling.

·         Do not change diapers near recreational water.

·         Do not go swimming or use hot tubs if you have diarrhea and for at least two weeks after diarrhea stops.

 

Reference

1.      ISDH November 13, 2004. Retail Food Establishments Sanitation Requirements. Title 410 IAC 7-24-122

      http://www.in.gov/isdh/21367.htm

2.      Norovirus Fact Sheet, Centers for Disease Control and Prevention,

www.cdc.gov/ncidod/dvrd/revb/gastro/norovirus.htm

3.      Quick Facts about Handwashing, Indiana State Department of Health,  

       http://www.in.gov/isdh/21085.htm