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Indiana Epidemiology Newsletter
Sandra Gorsuch, MS
ISDH Field Epidemiologist, District 5
On January 23, 2007, a representative of the Shelby County Health Department (SCHD) notified the Indiana State Department of Health (ISDH) that at least eight patrons who consumed food from a local restaurant developed acute gastroenteritis from January 20, 2007, through January 23, 2007.
The ISDH and the SCHD initiated a collaborative investigation to determine the cause of the outbreak and implement control measures to prevent further transmission of the illness. The ISDH developed a questionnaire to collect demographic information, as well as clinical and exposure histories of restaurant patrons and staff. A case was defined as any previously healthy person who consumed food at the restaurant or was epidemiologically linked to an individual who had consumed food at the restaurant and became ill with acute onset of vomiting or diarrhea on or after January 19, 2007. Eight individuals met the case definition (see Figure 1). None of the restaurant staff was reported as ill. The investigation revealed that eight patrons (100%) were experiencing nausea, vomiting, and diarrhea; five (62%) had low-grade fever. The median duration of the illness was 49 hours (range: 24 to 101 hours). The median incubation period was 16 hours (range: 8 to 44 hours). At least one person visited a hospital emergency department, but no one was hospitalized overnight. Four patrons submitted stool specimens to the ISDH Laboratories for analysis (see Laboratory Results).
The common food item eaten by seven of the eight ill patrons was salad (87%). There were no leftover food items available for analysis.
On January 23, 2007, a SCHD representative visited the food establishment to observe food preparation practices and inquire about restaurant staff illness. Management reported that none of the restaurant staff was ill. The SCHD representative noted that one of the restaurant staff wiped tables with an unsanitized towel and subsequently prepared a salad without tongs and before washing hands or wearing gloves. The SCHD recommended disinfecting restaurant environmental surfaces with 1:10 chlorine bleach to water solution; thoroughly washing hands with warm water and soap for at least 20 seconds before, during, and after food preparation; and wearing gloves when preparing food. Restaurant management implemented these corrective measures on January 23, 2007, after discussion of observed violations. No food samples were available for laboratory analysis.
The SCHD conducted a routine food inspection on February 5, 2007, and identified five critical violations of the Indiana Retail Food Establishment Sanitation Requirements (410 IAC 7-24). Critical violations included:
Except for the last violation, management implemented corrective measures on February 5, 2007, after the observed critical violations. The date-marking system for potentially hazardous ready-to-eat food was implemented on February 6, 2007.
Four patrons submitted stool specimens to the ISDH Laboratories for analysis. All specimens tested negative for Salmonella, Shigella, Campylobacter, and E. coli 0157:H7 by culture. All four specimens tested positive for Norovirus by reverse transcription-polymerase chain reaction (RT-PCR).
The investigation confirmed that an outbreak of viral gastroenteritis occurred at the Shelby County restaurant from January 20, 2007, through January 23, 2007. Eight cases, all restaurant patrons, were identified. The pattern of illness and closely-timed onset dates indicated a point source rather than person-to-person transmission. The one common reported exposure among all the cases was consuming food from the restaurant.
The causative agent of this outbreak was Norovirus. Four patrons tested positive and four additional patrons had characteristic Norovirus symptoms. The sudden, acute predominant signs and symptoms (vomiting, diarrhea, and nausea) and duration of symptoms (approximately 49 hours) reported in this investigation are typical of Norovirus outbreaks. Norovirus is characterized primarily by abrupt onset of nausea, vomiting and/or diarrhea, headache, body aches, chills, but little or no fever.¹ The incubation period for Norovirus is 24-48 hours. Illness usually resolves on its own within 1-2 days without complications. Dehydration may result after prolonged vomiting and diarrhea, particularly in young children, the elderly, and those with weakened immune systems. Norovirus infections typically occur during cooler months of the year (October to April) but can occur year-round.
Norovirus is thought to be responsible for 50 percent of all foodborne gastroenteritis outbreaks.² The mode of transmission is fecal-oral, and persons are infected by contaminated food or water, through close contact with an infected person, or contact with contaminated environmental surfaces and fomites. Because studies indicate Norovirus can become aerosolized during the cleaning process of infected vomitus and stool, it is recommended a mask be worn for protection while cleaning restrooms, vomitus, or stool. Norovirus, which is shed in stool, is highly contagious, and an infectious dose can be as little as 100 viral particles.¹ Persons with Norovirus usually become infectious when symptoms begin and can continue to shed virus in their stool for up to 2 weeks after symptoms cease. Up to 30 percent of individuals infected with Norovirus are asymptomatic. Norovirus survives chlorine up to 10 ppm (above levels recommended for swimming pools and public water systems) ¹ and temperatures below 32ºF and up to 140ºF. Although the virus does not multiply outside the human body, it can survive on environmental surfaces for 24-48 hours.
Foodborne outbreaks of Norovirus occur when food is contaminated by an infected food handler immediately before its consumption. Outbreaks have frequently been associated with consumption of ready-to-eat foods, including various salads, sandwiches, and bakery products. Semi-liquid items (e.g., salad dressing or cake icing) that allow virus to mix evenly are often implicated as a cause of outbreaks.²
No food specimens were obtained for laboratory analysis; however, 87 percent of the ill patrons reported eating salad. The SCHD representative observed unwashed, bare-hand salad preparation suggesting a possible route of contamination.
Most Norovirus outbreaks can be prevented by the following practices:
The Indiana State Department of Health extends its appreciation to the Shelby County Health Department for their quick response and professionalism. Their prompt and appropriate actions were instrumental in ending this outbreak.