Person-to-person outbreak masquerades as foodborne outbreak

What to know

Enteric outbreak investigations often require investigators to pivot their focus as new information is uncovered. When the source is unclear, investigators must use multiple investigative methods to determine how contamination occurred to prevent additional illnesses. New Hampshire’s Division of Public Health Services (DPHS), an OutbreakNet Enhanced site, exemplified this capacity to adapt when investigating an unknown outbreak.

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Person-to-person outbreak masquerades as foodborne outbreak

On March 29, 2022, New Hampshire DPHS received an initial complaint from a woman and her spouse. They reported experiencing gastrointestinal illness after consuming steaks from a local store. The food history obtained revealed that the couple also had recently attended a masquerade ball at an event center. Investigators visited the kitchen facility at the event space the same day as the reported complaint but did not find any food safety issues. After receiving additional complaints, investigators contacted the event organizer on April 1. They were able to obtain the event seating chart, food menus, and contact information for 37% of the 331 event attendees. The event organizer also informed the investigators that they had received direct complaints of illnesses from masquerade attendees.

Investigators deployed an electronic survey via email to reach as many attendees as possible. The survey included questions about food consumption and symptoms of gastrointestinal illness before and after the event. The results of the survey were analyzed for any suspected sources of contamination. Wild rice was initially suspected, but analysis results were not statistically significant, so it was not likely the cause of illnesses. No other food items or information collected by the surveys stood out to the investigators.

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New Hampshire DPHS deployed an electronic survey to reach as many event attendees as possible.

In addition to interviewing, an environmental assessment was conducted at the establishment to gather information on meal preparation and food-handling methods. The facility appeared clean and no staff had reported being sick during the event or afterwards. New Hampshire Public Health Laboratories did not receive clinical or food samples, so sequencing results could not be used to guide the investigation.

New information

Investigators had their first break after an event attendee reached out to New Hampshire DPHS directly. The attendee described witnessing suspected fecal matter on the dancefloor and vomit in the restrooms during the event. With this new information, investigators contacted the event organizers again. During their call, investigators learned that the organizers had been made aware of this shortly after the event. The organizers had not initially shared this information as they were unsure if these observations should be shared with public health.

After this discovery, investigators were able to surmise that the outbreak was most likely caused by person-to-person transmission. Contagious particles could easily have been spread by being transferred to clothing, shoes, and bare feet, causing individuals to become sick. Unfortunately, no ill attendees submitted specimens for testing, so the source of the outbreak could not be confirmed. However, given the likely mode of transmission, norovirus was suspected to be the likely cause of outbreak at the masquerade ball. The withheld information likely slowed investigation efforts, but investigators were able to refocus from a foodborne to a person-to-person transmission investigation.

Conclusion

New Hampshire DPHS investigators were able to exhaust all sources of information to identify the likely source of illness in this investigation. At the end of the investigation, investigators reinforced the importance of communication between public health officials and event organizers. This investigation also reinforced the importance of thorough communication with establishments to ensure all relevant information is captured during initial interviews with a facility. Additionally, the facility was reminded of the importance of having policies for cleaning-up after vomiting and diarrhea events to prevent contamination. Lastly, investigators provided broader recommendations in response to this outbreak, as well as universal recommendations for outbreak investigations. Communication and capacity to pivot investigative efforts and focus are crucial in responding to outbreaks more effectively and preventing future reoccurrence.