On April 26, 2013, the Southern Nevada Health District (SNHD), Office of Epidemiology (OOE) received reports of gastrointestinal illness from eight independent groups of patrons of Firefly on Paradise or the adjacent affiliated restaurant Dragonfly on Paradise (Firefly) located at 3900 Paradise Road, Las Vegas, NV 89109. All patrons from these groups ate at the restaurant during April 21-24, 2013. Ill patrons reported symptoms of diarrhea and/or vomiting after they consumed food from Firefly restaurant, and many sought medical care for their illness. In response to these illness reports, the SNHD initiated an investigation.
On April 26, 2013, the SNHD performed investigative inspections and closed Firefly and Dragonfly restaurants to minimize ongoing risk of illness. The SNHD OOE, Environmental Health (EH) and Southern Nevada Public Health Laboratory (SNPHL) have been collaborating on the investigation and response to this outbreak. The Centers for Disease Control and Prevention (CDC), the United States Department of Agriculture (USDA), and the Nevada State Health Division (NSHD) were also notified of the outbreak investigation.
Epidemiology
A probable case is defined as illness in a person who consumed food served by Firefly restaurant during April 21-26, 2013, experienced diarrhea (defined as ≥ 3 bouts of loose stools) and/or ≥ 1 episodes of vomiting during a 7-day period after eating, and reported the illness to SNHD no later than end of day May 13, 2013 (midnight). The case definition for confirmed cases was not changed.
Laboratory
SNPHL continued its normal procedures of receiving Salmonella isolates from local laboratories and performing speciation and pulsed field gel electrophoresis (PFGE) testing on them. SNPHL is sending Salmonella isolates associated with the outbreak to CDC for multiple-locus variable number tandem repeat analysis (MLVA), a method used to perform molecular typing of particular microorganisms to study possible transmission routes and sources of infection.
Environmental Health
After communication with NSHD, USDA’s Food Safety Inspection Service (FSIS) plans to perform a trace-back of a cooked food item identified as having been contaminated with the outbreak species of Salmonella.
Results
The epidemic curve as of May 20, 2013 shows a total of 294 people whose illnesses met the case definition (73 confirmed and 221 probable cases). All identified ill persons ate at Firefly during April 21 through April 26, 2013. Illness onset dates occurred within the April 22 to May 1, 2013 time frame.
From various surveillance data sources, we have received reports of illness from restaurant patrons who normally reside in 27 states and two foreign countries (Canada and United Kingdom) who ate at Firefly during their visits to Las Vegas.
Laboratory
As of May 20, 2013, the following laboratory activities have occurred. In addition to 14 specimens initially collected and tested by SNHD, of which 12 were positive for the outbreak strain of Salmonella, local microbiology laboratories have submitted to the SNPHL 83 Salmonella isolates obtained from Clark County residents. Among them, serotyping and PFGE analyses have been completed on 74 of these samples, with the remaining nine samples still pending serotyping and PFGE analyses. Of the 74 samples, 61 had PFGE patterns matching the outbreak strain and were from specimens collected from persons whose illnesses met the case definition. These 61 PFGE patterns were sent to CDC’s PulseNet program to determine if they are related to other common source outbreaks in the U.S. To date, PulseNet results have identified no concurrent U.S. cases of salmonellosis matching the outbreak strain other than those linked to the Firefly restaurant.
SNPHL has sent 6 Salmonella isolates to CDC for testing by the National Antimicrobial Resistance Monitoring System (NARMS) program. Results are pending. SNPHL has sent 49 Salmonella isolates to CDC for MLVA. Results are pending.
Of the 21 food items that were analyzed and are shown in the table below, one item, cooked chorizo (a type of sausage), tested positive for Salmonella. Culture and PFGE-pattern results of the Salmonella isolate obtained from the cooked chorizo matched those of the outbreak strain. There are no plans to test the remaining 14 food items that were collected on April 26, 2013.
Environmental Health
EH staff contacted Firefly restaurant management to gather more information about the handling of the chorizo product. The chorizo came into the restaurant raw and was subsequently cooked by Firefly restaurant staff. All chorizo items collected from Firefly by EH and tested were already cooked by restaurant staff. No raw chorizo was collected by EH in the initial inspection.
Initially, we attempted to trace back some food products that either arrived raw to the restaurant or were served uncooked to patrons to try to identify how a food could have become contaminated at its source or during delivery, storage or preparation. However, in light of the laboratory result that the outbreak strain of Salmonella was isolated from the cooked chorizo, trace-back efforts have been redirected at the chorizo products due to a small possibility that raw chorizo was contaminated prior to arriving at Firefly.
Discussion
As of May 20, 2013 at least 290 patrons and four employees who consumed food and/or drinks at Firefly restaurant during April 21-26, 2013 have been identified to be confirmed or probable cases of Salmonella infection. No illness has been reported among staff or patrons of the other Firefly restaurants located in Clark County (Firefly Westside and Firefly on Eastern). The rate of cases being reported to SNHD has declined significantly with no evidence of any disease transmission after the closure of the restaurant on April 26, 2013. It is possible that the number of cases will change slightly over the next weeks as the last laboratory results arrive that either identify new confirmed cases, or eliminate probable cases from our count should they fail to have PFGE patterns matching the outbreak strain.
No concurrent cases of salmonellosis having a PFGE pattern matching the outbreak strain have been identified in the U.S. other than those linked to the Firefly on Paradise restaurant.
It is likely that the outbreak was due to local cross-contamination in the restaurant’s kitchen and not from a contaminated commercial food.
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