By Ethan Covey

A March 2022 outbreak of influenza A(H3N2) following an off-campus school banquet in Los Angeles County, resulted in nearly half of attendees falling ill (MMWR 2022;[71]:745-746).

“This outbreak shows that flu viruses can spread easily among people during large social gatherings, and flu viruses have the potential to cause outbreaks of respiratory disease as COVID preventive measures are being lifted across the county,” said Lello Tesema, MD, an internal medicine specialist with the Los Angeles County Department of Public Health (LACDPH).

A total of 184 people—177 students and seven teachers—attended the banquet. Three days later, an outbreak of acute respiratory illness was reported to LACDPH. Flu symptoms, including fever, cough, headache and fatigue, were reported by 41% of the students. Four students received treatment at an urgent care facility, but none were hospitalized.

Nearly all (95%) of attendees completed testing for respiratory pathogens, and 32% received a positive test result indicating influenza A(H3N2) infection. Due to the high transmission rate, the school was temporarily closed to in-person attendance.

While flu activity has remained low during the pandemic, increases have been observed, particularly as mitigation strategies are relaxed.

“Flu activity in this L.A. County community had more than tripled in the weeks leading up to the outbreak, and local mandates for face masks and physical distancing were lifted in the community and at the school in the weeks leading up to the outbreak,” Dr. Tesema said.

Dr. Tesema noted the importance of influenza vaccines, in combination with hygiene practices, in preventing disease spread.

“CDC recommends a yearly flu vaccine and everyday preventive actions, like handwashing, covering coughs and sneezes, and staying home when sick to prevent flu,” she said. “Medical providers should consider the possibility of influenza in patients with respiratory disease, given ongoing late season influenza activity in the U.S.”