The first HPAI H5N2 infected flock in Minnesota was identified in March 2015. The virus spread to 110 premises (104 commercial turkey flocks, 5 chicken layer flocks, and 1 backyard flock) in 23 counties before the outbreak ended in mid-June 2015, making Minnesota the U.S. state with the greatest number of infected flocks during this HPAI outbreak. Over 8.8 million birds died or were depopulated to limit disease spread.^4,5 Molecular analysis later showed that spread involved a combination of individual point source introductions of the virus from wild waterfowl and substantial farm-to-farm spread, particularly later in the outbreak.^{3, 6–8} The economic burden due to the outbreak was over $650 million, and 2,500 jobs in Minnesota were impacted.^4,9 The emotional toll on producers, responders, and state animal and human health officials was immeasurably large.

In 2022–2023, the Midwest was again the most affected region in the U.S. by HPAI. In Minnesota, HPAI H5N1 was identified in nearly every county of the state, with 115 commercial flocks (including 112 commercial turkey flocks, two chicken layer flocks, and one chicken broiler operation) and 36 backyard flocks infected from March 25, 2022 to December 31, 2023. Over 6.3 million birds died of the disease or were depopulated to prevent disease spread.¹⁰ Molecular analysis determined that cases in domestic poultry in 2022–2023 occurred almost entirely through individual introductions of the virus from wild birds to poultry flocks, rather than from farm-to-farm spread.^11–13 This molecular evidence aligned with the extraordinary number of HPAI detections in wild birds and the large number of backyard flocks infected, which typically have more contact with wild birds than commercial flocks.^14,15

Minnesota is known among affected states for its truly One Health approach to HPAI outbreak response in domestic poultry. The Minnesota Board of Animal Health (BAH), Minnesota Department of Agriculture (MDA), Minnesota Department of Natural Resources (DNR), Minnesota Department of Health (MDH), and United States Department of Agriculture (USDA) collaborate as full partners in HPAI response including real-time communication as events unfold. This manuscript describes the Minnesota Department of Health’s (MDH) surveillance methods and outcomes, and public health response activities during the 2015 and 2022–2023 HPAI outbreaks, focusing on successes, challenges, and lessons learned that may be of value to other public health responders.

The most important role of MDH in the 2015 and 2022–2023 HPAI outbreaks was to protect human health, which was the source of the agency’s statutory authority to act. HPAI is an animal disease emergency; therefore, MDH supported the responding animal health agencies and was not the lead agency in the joint response. In 2022–2023, to streamline information sharing, MDH’s State Public Health Veterinarian (SPHV) and Deputy SPHV served as human disease surveillance officers on the Minnesota HPAI Incident Management Team (IMT) (Figure 1). Inclusion in the IMT was codified during multi-agency after-action reviews held after the 2015 HPAI outbreak to ensure more efficient access to situational information in real time going forward.

The basic functions of MDH during both outbreaks were to provide guidance on infection control and use of personal protective equipment (PPE); individually interview poultry workers, responders, and others in contact with infected birds for work duties, type of contact, PPE usage, and illness history; institute active human disease surveillance for signs of avian influenza illness among exposed people, known as “monitoring;” test any symptomatic people for influenza; provide information about human health risk and disease prevention to poultry workers, industry partners, incident responders, and the public in multiple formats; and when appropriate, recommend human seasonal influenza vaccination.

Minnesota Board of Animal Health (BAH) contacted the MDH Zoonotic Diseases Unit (ZDU) by email as soon as a flock was identified as presumptively positive for HPAI at the Minnesota Veterinary Diagnostic Laboratory, and before the flock was confirmed positive at the National Veterinary Services Laboratory. Starting in 2022, BAH case managers, usually the first responder on a HPAI-positive farm, distributed MDH’s “Health Information for Poultry Personnel” handout, which was created during the 2015 outbreak (Appendix 1). The handout provided guidance on recommended PPE inside the poultry buildings, information on monitoring, contact information for MDH, and mental health resources. It was translated into Spanish, Karen, Hmong, and Somali, and modified in 2022 for additional audiences including backyard flock owners, wildlife rehabilitators, and incident responders. Callers to the BAH Sick Bird Hotline (a telephone number provided to the public for reporting potential HPAI-infected backyard flocks) were verbally advised about MDH recommendations for PPE and emailed a “Health Information for Backyard Flock Owners” handout.

In 2015, MDH staff contacted the flock owner or manager to identify everyone who had contact with an infected flock. Starting in 2022, for company-owned commercial flocks (vs. independently-owned commercial flocks), MDH contacted the company’s occupational health or safety lead to obtain contact information for all employees associated with an affected premises. Participation in monitoring by workers was voluntary. However, when farm owners, managers, or company occupational health and safety leads were contacted by MDH, it was expected they would provide the names and contact information for personnel associated with an infected premise. ZDU staff then attempted to contact all potentially exposed people and conduct a standardized interview regarding their role on the farm, what type of contact they had with sick birds, what type of PPE they were using, whether they considered themselves to be immunocompromised, and answered any questions workers had. Interviews were conducted in the participant’s preferred language, either with native speakers employed at MDH or through a contracted interpreter service. Based on their interview, each person was evaluated for risk of severe disease with influenza by assessing their level of exposure to infected birds in the context of self-reported PPE usage and any immunocompromising conditions. People were considered exposed if they had entered a barn with poultry on an HPAI test-positive premises in the 2 days before the first indication of illness in the birds, or anytime thereafter (or) in the 2 days before the collection date of the first positive test samples, or anytime thereafter until depopulation was complete. This included people who worked with healthy flocks on the same premises. Anyone considered exposed was entered into monitoring with their consent. People who may have been on a test-positive premises but did not enter any of the poultry buildings were not considered at risk and were not monitored. In 2015, MDH monitored the health of poultry workers only and one backyard flock owner. In the 2022–2023 response, MDH monitored the health of poultry workers; backyard flock owners; BAH, MDA, and USDA responders; and private contract workers, as well as tracked the number of different infected premises to which an individual was exposed during each outbreak.

During both time periods, the first interview was conducted via telephone. The monitoring period was 10 days from the last exposure, but the number of times MDH contacted the person during monitoring depended upon the person’s role in the response and the level of exposure in the context of self-reported PPE usage. In 2015, monitoring was paper interview-based, data were maintained in an Excel spreadsheet, and texting was the default monitoring contact method. MDH ZDU public health graduate student workers texted poultry workers individually 7 days/week and sent personalized messages to each worker. In 2022–2023, in an effort to improve data integrity and the sustainability of the response in terms of staff hours, interview responses were entered into a REDCap (Research Electronic Data Capture) database in real time, which automatically entered the person into monitoring if they consented. Through REDCap, they received an automated email with a unique link to a two-question survey asking about any symptom development or further contact with a subsequent infected flock. Follow up by phone or text was also available by request.

During both outbreaks, full PPE use was defined as the continuous use of all the following elements of PPE: washable or disposable long-sleeved coveralls or Tyvek suit; rubber boots that could be disinfected or disposable plastic boots; washable or disposable head covering or Tyvek suit hood; latex or nitrile gloves; eye protection; and an N95^® filtering facepiece respirator (N95^®), or KN95^® respirator if an N95^® respirator was not available. Medical clearance and fit testing were encouraged. During the 2022–2023 response only, if an individual reporting missing or inconsistent PPE use, they were asked if they lacked access to necessary PPE components.

Individuals who were exposed to infected flocks, including being present in infected barns and/or physically touching birds or their environment, without full PPE and who self-identified as immunocompromised were referred to their healthcare provider to discuss antiviral prophylaxis. With the individual’s consent, MDH facilitated the process by working with the individual’s health care provider or the company occupational health department, which included providing CDC’s current antiviral prophylaxis recommendations. CDC’s threshold for recommending prophylactic antivirals after exposure to infected flocks was higher in 2022–2023 than in 2015, though in both outbreaks, prophylaxis could be considered after any unprotected exposure.^16,17 Anyone who reported symptoms was referred to MDH’s Vaccine Preventable Diseases Surveillance Unit for follow-up and testing, which was limited to Influenza A in 2015. In 2022–2023, testing was expanded to include a multi-pathogen respiratory panel. Evaluation and sampling of the individual was normally performed at a local primary care clinic and facilitated by MDH.

Data analyses were performed using SAS 9.4 (SAS Institute, Cary, NC, USA) statistical software. Descriptive statistics from the 2015 HPAI outbreak were analyzed and compared to descriptive statistics from the 2022–2023 HPAI response where appropriate. Study data were collected and managed using REDCap electronic data capture tools hosted at the Minnesota Department of Health.^18,19 During the 2022–2023 response, individuals were only interviewed once per response season (i.e., Spring 2022, Fall 2022, Spring 2023, Fall 2023). However, the same individual could have completed multiple interviews if they were exposed to poultry during subsequent seasons. Analyses were conducted on the differences in PPE utilization and vaccination rates among poultry workers in 2015 and 2022–2023, using the initial interview as their baseline. Dichotomous variables were analyzed using a chi-square test or Fisher’s exact test as applicable. A p-value <.05 was considered significant.

From March 3 to June 5, 2015, MDH ZDU epidemiologists interviewed, evaluated, and monitored 375 (85.8%) of 437 poultry workers from 110 infected flocks (Table 1). Of the workers interviewed, 198 (52.8%) individuals were recommended by MDH epidemiologists to take prophylactic oseltamivir based on their exposure to test-positive premises without the use of full PPE, or if they had risk of severe disease from influenza. Of these, 118 (59.6%) agreed to take prophylactic antivirals, and the remaining chose to refrain unless symptoms developed. An interpreter was utilized for 11 Karen-speaking and 10 Spanish-speaking poultry workers. Among poultry workers, 221 (59%) chose texting versus a telephone call or email for monitoring their health.

In 2015, 186 (51.8%) of 359 poultry workers reported consistently using all recommended PPE components, among those who did not, eye protection compliance was lowest (Table 2). When poultry workers employed in a turkey breeding facility, where use of full PPE is typically required, were removed from analysis, 96 (35.7%) of 269 poultry workers reported wearing full PPE (Table 2). A human seasonal influenza vaccination in the past season was reported by 132 (47.0%) of 281 poultry workers. There were 20 (5.3%) poultry workers who reported respiratory symptoms; 15 consented to medical evaluation and were tested only for Influenza A. Among those tested, no human infections with avian influenza were identified (Table 3).

From March 25, 2022 to December 31, 2023, MDH ZDU staff interviewed and evaluated 649 (65.4%) of 992 poultry workers, state and federal responders, contractors (private environmental health company workers and poultry company depopulation teams), and backyard flock owners associated with 151 infected flocks (Table 1, Figure 2). Among the 343 (34.6%) individuals potentially at risk who refused an interview or were lost to follow-up, the greatest proportion were contractors (134 (61.4%) of 218 contractors), followed by poultry workers (196 [30.9%] of 635), and state and federal responders (13 [17.3%] of 75). All 64 backyard flock owners were contacted and agreed to be interviewed (Table 1).

Among the 649 interviews, 536 (82.6%) interviewees met the criteria for monitoring based on having entered poultry buildings on an infected premise. Of 514 interviewees who consented to monitoring, 134 (26.1%) elected to be contacted by text message instead of the standard e-mail monitoring. Individuals were only interviewed once per response season (i.e., Spring 2022, Fall 2022, Spring 2023, Fall 2023), but the same individual could have completed multiple interviews, if they were exposed to poultry during subsequent seasons. During 2022–2023, there were 469 unique individuals involved in the outbreak, including 309 poultry workers, 60 contractors, 36 state and federal responders, and 64 backyard flock owners (Table 1, Figure 2). Contractors and state and federal responders who responded to multiple infected premises (n = 50) accounted for 10.7% of 469 at-risk people and 22.9% ( n = 218) of 950 exposures (data not shown).

In 2022–2023, 134 (28.6%) of 469 at-risk individuals who met monitoring criteria reported wearing all recommended elements of PPE; among those who did not, eye protection was most often not used (Table 2). Among poultry workers specifically, 74 (23.9%) of 309 reported consistently using all recommended PPE components (Table 2). When poultry workers employed in a turkey breeding facility, where use of full PPE is typically required, were removed from analysis, 59 (23.0%) of 257 poultry workers reported wearing full PPE (Table 2). Among individuals who reported not using full PPE, 41 (12.2%) of 335 reported the reason for that being a lack of access to all components. A human seasonal influenza vaccination in the past season was reported by 102 (33.1%) of 308 poultry workers (Table 2).

In 2022–2023, 45 (8.4%) people reported illness with respiratory, ocular, or gastrointestinal (GI) symptoms, 37 (82.2%) of whom were recommended to undergo testing for respiratory and GI pathogens. Of those, 24 (64.9%) agreed to testing. While H5N1 HPAI was not detected, several other human respiratory viruses and GI pathogens were found (Table 3).

In 2015, as the outbreak rapidly grew, data management and analysis became increasingly more challenging. In 2022–2023, before the first infected flock was detected in Minnesota, MDH prepared a REDCap database, automatic email-based monitoring system, and response protocols to enhance data management and sustainability. As a result, many direct comparisons between the two responses were not possible. More turkey breeding facilities were impacted in 2015 than in 2022–2023, impacting PPE usage and influenza vaccine data because full PPE usage is standard and required, and influenza vaccine is provided to workers in the turkey breeding industry. We strove to mitigate this by excluding poultry workers employed in turkey breeding operations from the PPE by outbreak analysis, but it was not possible for the influenza vaccination comparison because the vaccine is not required, only supported. There was likely response bias, as individuals willing to be interviewed and participate in monitoring may also be more likely to use PPE and participate in other protective behaviors such as vaccination. In 2022–2023, the largest proportion of workers/responders lost to follow-up were contractors. Some contract-workers, especially migrant workers, may have been reluctant to engage with government officials, thus impacting our findings, particularly on PPE usage, as contractors may have a higher likelihood of working in unsafe conditions that may include a lack of PPE or training on proper PPE use.³²