Situation Report: Latest Cases of H5N1

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Recent Reports of H5N1 in Cambodia

Last week, Cambodia reported two fatal cases of human infection with H5N1 (CDC, https://www.cdc.gov/flu/avianflu/spotlights/2022-2023/cambodia-two-fatal-H5N1.htm, Accessed 10/20/2023) avian influenza: a 2-year-old girl from Prey Veng province and a 50-year-old man from neighboring Svay Rieng province. Both cases likely resulted from exposure to infected poultry. There is no indication of person-to-person spread, however close contacts of both patients, including potentially exposed health care workers, are being monitored closely. 

The last reported cases in Cambodia came in February 2023: a fatal H5N1 case in an 11-year-old girl from Rey Veng provinces and her father who was asymptomatic. These four cases are Cambodia’s first H5N1 infections since 2014. 

H5N1 Viruses Circulating Globally

Genetic sequencing of samples from all four patients revealed that the virus belongs to the 2.3.2.1c clade, similar to viruses that have been circulating in birds and poultry in the region over the past decade. This is different than the 2.3.4.4b clade that continues to circulate in wild birds, poultry, and some mammals, and which has been linked to the majority of human infections with H5N1 since 2022 (CDC, https://www.cdc.gov/flu/avianflu/spotlights/2022-2023/h5n1-technical-report_september.htm#table1, Accessed 10/20/2023). 

Since the first human infections were detected in 1997, a total of 900¹ sporadic human H5N1 cases have been reported from 22 countries. Nearly all reported human infections with H5N1 have had recent exposure to sick or dead poultry. Rare, limited, and non-sustained person-to-person transmission has occurred, likely due to prolonged unprotected close exposure to symptomatic persons. 

Because of the potential for influenza viruses to rapidly evolve and the global prevalence of H5N1 viruses in wild birds and poultry, continued sporadic human infections are anticipated. 

Recommendations for Health Care Personnel

While the Centers for Disease Control and Prevention (CDC) has assessed the current risk to the public as low, health care personnel should follow CDC’s recommendations for patient evaluation, treatment, and testing of avian influenza A viruses, including H5N1 (CDC, https://www.cdc.gov/flu/avianflu/clinicians-evaluating-patients.htm, 10/20/2023).

Patient Evaluation

Screen patients for signs and symptoms of influenza-like illness, including fever, cough, sore throat, runny or stuffy nose, muscle or body aches, headaches, fatigue, conjunctivitis, shortness of breath or difficulty breathing. Less common signs and symptoms are diarrhea, nausea, vomiting, or seizures. 

See the case definitions of confirmed, probable, and suspect cases (CDC, https://www.cdc.gov/flu/avianflu/case-definitions.html, Accessed 10/20/2023) of infection with avian influenza A.

Preventing the Spread of Infection During Patient Care

• Ask symptomatic patients to put on a facemask when they enter the facility. 
• Place the patient in an airborne infection isolation room (or if unavailable, a single room with the door closed).
• Implement Airborne and Contact Precautions with the use of eye protection, in addition to Standard Precautions. 

For more information on recommended infection prevention and control measures, visit Infection Control Within Healthcare Settings for Patients with Novel Influenza A Viruses (CDC, https://www.cdc.gov/flu/avianflu/novel-flu-infection-control.htm, Accessed 10/20/2023).

Treatment and Care

The CDC currently recommends initiating antiviral treatment as soon as possible for outpatient and hospitalized patients who are suspected, probable, or confirmed to be infected with avian influenza A. Antiviral treatment should not be delayed while waiting for laboratory test results. Find additional treatment guidance (CDC, https://www.cdc.gov/flu/avianflu/novel-av-treatment-guidance.htm, Accessed 10/20/2023).

Testing Considerations

If the patient has signs and symptoms of infection and possible exposure to H5N1 virus, you should collect respiratory specimens for testing. Rapid influenza tests may detect HPAI but will not distinguish between seasonal influenza and HPAI. Respiratory panels that distinguish influenza subtypes may detect HPAI but will give an “unsubtypeable” result. Specimens from patients possibly exposed to H5N1 virus or that test positive for an influenza A virus with an “unsubtypeable” result should be sent to a state or local public health laboratory for further testing. 

Learn more about laboratory testing, specimen collection, and shipping for avian influenza.

Vaccines

Several candidate vaccines to prevent infection with H5N1 have been developed but none are yet available for widespread use.

H5N1 Resources for Health Care Personnel

Watch the NETEC webinar “H5N1 for Health Care Personnel” to learn more about the epidemiology of human cases of H5N1 and risk factors, antiviral treatments, and clinical management of patients infected with H5N1 virus. This webinar is also available for continuing education credits.

1. The CDC report updated on October 5 lists a total of 898 cases, which does not include the two most recent cases in Cambodia.