Cluster of Influenza A(H5) Cases Associated with Poultry Exposure at Two Facilities — Colorado, July 2024

Investigation and Results

Public Health Notification and Response

On July 8, 2024, poultry in a commercial egg-layer operation in northeast Colorado (facility A)* were confirmed to have highly pathogenic avian influenza (HPAI) A(H5N1).^† Facility A hired approximately 250 contract workers to conduct depopulation (i.e., euthanasia) of all poultry on the premises, which began on July 9. On July 11, the Colorado Department of Public Health & Environment (CDPHE) and Colorado Department of Agriculture were notified of several ill workers. Based on potential exposure and symptoms consistent with influenza A(H5N1) virus infection, a field team was mobilized to conduct testing among symptomatic workers and offer them empiric treatment with the influenza neuraminidase inhibitor oseltamivir (75 mg twice daily for 5 days). Seven workers reported symptoms and received testing on July 11, and 45 symptomatic workers received testing on July 12; all received oseltamivir. To ensure an adequate supply of the recommended personal protective equipment (PPE) for exposed workers (1), CDPHE delivered goggles, N95^§ filtering facepiece respirators (FFRs), and nitrile gloves to facility A on July 12. On July 13, a small team returned to determine PPE-use practices during work activities.

Because many workers had symptoms, including several who received presumptive positive test results for influenza A(H5),^¶ and because observed PPE compliance was low, CDPHE distributed oseltamivir to all workers as postexposure prophylaxis (PEP),** irrespective of symptoms. On July 15 and 16, an on-site team conducted symptom screening, testing for symptomatic workers, and distribution of oseltamivir; 13 additional workers with symptoms received testing and empiric treatment, and 219 workers received a 10-day course of oseltamivir PEP.^†† CDPHE returned to facility A on July 23, and identified no additional workers with symptoms.

On July 14, 2024, CDPHE was notified that poultry at facility B, located in the same county as facility A, had a nonnegative test result^§§ for influenza A(H5). CDPHE delivered goggles and N95 FFRs to facility B on July 15. Facility B commenced poultry depopulation on July 15, with approximately 400 contract workers participating. The facility initially reported no illness among workers and high PPE compliance. Therefore, oseltamivir PEP was not offered. Instead, CDPHE established routine screening and offered testing and empiric oseltamivir treatment (75 mg twice daily for 5 days) during six visits^¶¶ to 44 workers experiencing symptoms.

Between CDPHE site visits, staff member team leads at facilities A and B conducted screening among workers before shifts based on guidance from CDPHE. Facility A identified no additional symptomatic workers after July 16. Facility B reported two symptomatic workers during facility-led screening; both workers declined testing and empiric oseltamivir treatment. As depopulation activities concluded, CDPHE visited both facilities to distribute cards providing information in English and Spanish about symptoms of avian influenza A virus infection in humans, where to seek care if workers became ill, and information for health care providers regarding workers’ exposure to H5N1-infected poultry.

Screening and Testing Among Workers

Workers conducting poultry depopulation, carcass removal, and disposal were asked if they were feeling ill. Those with self-reported symptoms were asked to complete a brief questionnaire including information on exposures, symptom onset, specific symptoms,*** and PPE use.^††† Nasopharyngeal swabs and conjunctival swab specimens were collected from workers reporting symptoms; swab specimens were tested for influenza A and A(H5) virus at the CDPHE laboratory. Specimens testing negative for influenza A and A(H5) virus were tested for SARS-CoV-2.^§§§ Specimens testing presumptively positive for influenza A(H5) virus or with inconclusive results were sent to CDC for confirmatory testing. This activity was reviewed by CDC, deemed not research, and was conducted consistent with applicable federal law and CDC policy.^¶¶¶

CDPHE screened 663 workers for symptoms during July 11–July 26, 2024. The median age of workers was 30 years (range = 15–56 years), and most spoke only Spanish. At facility A, 65 (25%) of 265 workers who received screening reported symptoms and received testing, and six (9%) of 65 (2.3% of all workers) received a positive influenza A(H5) test result (Table 1). At facility B, 44 (11%) of 398 workers who received screening reported symptoms and received testing, and three (7%) of these 44 workers (0.8% of all workers) received a positive influenza A(H5) test result. Among those who received a negative influenza A and A(H5) test result, one worker at facility A and 18 at facility B received a positive SARS-CoV-2 test result. Symptom onset date was known for 25 (38%) of 65 workers at facility A and 39 (89%) of 44 workers at facility B (Figure).

PPE Use Among Workers Who Were Symptomatic

Self-reported PPE use among workers who were symptomatic varied by facility. At facility A, workers reported lowest usage for boots or boot covers (18%) and highest usage for masks (49%). At facility B, workers reported lowest usage for head covers (77%) and highest usage for masks (100%).

Clinical Description of Human Influenza A(H5) Cases

All nine workers who received positive influenza A(H5) test results completed the questionnaire at the time of testing, and eight were reached for detailed interviews after receipt of their positive test result. Five cases occurred among women and four among men. The median age was 32 years (range = 18–56 years). Two patients had diabetes, one had asthma, and one was a longtime smoker. All reported direct contact with sick or dead poultry during depopulation and carcass disposal activities. Symptom onset occurred a median of 1 day after initial occupational exposure (range = 1–8 days),**** and symptomatic workers received testing a median of 2 days after symptom onset (range = 0–3 days). All nine patients reported conjunctivitis, seven reported eye tearing, and six reported subjective fever or chills. All patients reporting subjective fever or chills worked at facility A. Respiratory symptoms such as sore throat, cough, and shortness of breath were less frequently reported (Table 2). All patients received oseltamivir treatment. Symptoms resolved for seven patients a median of 4 days after onset (range = 1–8 days). Two patients interviewed 2 days after symptom onset reported ongoing or improving conjunctivitis; however, these persons were not able to be interviewed again. No hospitalizations or deaths occurred; one patient sought outpatient medical care for conjunctivitis on the day of symptom onset. Four patients remained symptomatic and were retested 1–5 days after receipt of their initial positive test result; none received a positive follow-up test result. Among the nine workers who received a positive test result for influenza A(H5), both nasopharyngeal and conjunctival swabs were positive for three, only the conjunctival swab was positive for five, and only the nasopharyngeal swab was positive for one. Virus was successfully isolated from specimens from five infected workers, codon complete genomes were successfully sequenced for four cases, and six of eight gene segments were successfully sequenced for one, identifying the viruses as clade 2.3.4.4b genotype B3.13.