RESULTS OF SYMPTOM MONITORING AMONG PERSONS EXPOSED TO HIGHLY PATHOGENIC AVIAN INFLUENZA (HPAI) A H5N1, FEBRUARY 7 - JULY 30, 2022, UNITED STATES

Highly pathogenic avian influenza (HPAI) A H5N1 viruses belonging to clade 2.3.4.4.b have become the predominant circulating avian influenza strain in birds throughout much of the world including Europe, Africa, and the Middle East beginning in 2021. This virus was first identified in birds in North America in December 2021 in Canada and first identified in the United States in January 2022 in a hunter-harvested wild bird in South Carolina. As of July 30, 2022, there have been detections in wild birds in 44 U.S. states and outbreaks in commercial poultry farms or backyard/hobby flocks in 38 U.S. states. In order to better understand the risk to human health, symptom monitoring of exposed individuals was instituted in the United States to detect any human infections. The U.S. Centers for Disease Control (CDC) recommends active symptom monitoring for individuals exposed to birds known to infected with HPAI A H5N1 or their environment for a period of 10 days following exposure (particularly among those without recommended personal protective equipment). Each jurisdiction defined and applied monitoring criteria according to their needs and capacity. Symptom monitoring was conducted by state or local health departments by contacting exposed individuals either daily, or on days 0, 5, and 10 after exposure. If individuals developed signs and symptoms compatible with avian influenza during the monitoring period, respiratory specimens were collected and tested for avian influenza at state public health labs. State health departments reported the numbers of individuals they had monitored and tested to CDC weekly. During February 7- July 30, 2022, the U.S. National Veterinary Services Laboratory confirmed 209 outbreaks in backyard flocks and 189 outbreaks in commercial flocks as HPAI A H5N1. Among the 4,424 people reported to have been exposed to infected birds, 124 (2.8%) reported symptoms consistent with avian influenza virus infection. All symptomatic individuals reported mild illness. One individual was positive for avian influenza A H5N1. Despite having over 4,000 persons exposed to HPAI A H5N1 in birds across the United States, H5N1 was only detected in one person through symptom monitoring and testing. The low influenza A H5N1 test positivity among people in active monitoring suggests that the overall risk of influenza A H5N1 infection for people that were exposed to infected birds is low for the current circulating clade.