Awareness of currently circulating viral illnesses is essential for effective infection prevention and control. This winter brings evolving challenges with Avian influenza A (H5N1) (“H5N1 bird flu”), norovirus, and human metapneumovirus.
This guide provides a concise overview of symptoms, diagnostics, infection control best practices, and clinical management strategies to help healthcare providers and infection preventionists address these pathogens effectively. As always, expert consultation with an infectious diseases provider is recommended for complicated cases.
Avian Influenza A(H5N1) illness (“H5N1 bird flu”)
Bird flu (avian influenza) is an infection from a type of influenza (flu) virus that usually spreads in birds and other animals. While the current public health risk is low, CDC is watching the situation carefully and working with states to monitor people with animal exposures.
Symptoms:
- People with signs and symptoms consistent with acute upper or lower respiratory tract infection, conjunctivitis or complications of acute respiratory illness without an identified cause. In addition, gastrointestinal symptoms such as diarrhea are often reported with H5N1 infections.
- Mild symptoms – cough, sore throat, eye redness or eye discharge such as conjunctivitis, fever or feeling feverish, rhinorrhea, fatigue, myalgia, arthralgia, headache
- Moderate-severe symptoms: shortness of breath or difficulty breathing, altered mental status, seizures
- Complications: pneumonia, respiratory failure, acute respiratory distress syndrome (ARDS), multi-organ failure (respiratory and kidney failure), sepsis, meningoencephalitis
Diagnostic Tests:
People exposed to H5N1-infected birds or other animals (including people wearing recommended PPE) should be monitored for signs and symptoms of acute respiratory illness beginning after their first exposure and for 10 days after their last exposure.
- Laboratory Testing:
- Reverse-transcription polymerase chain reaction (RT-PCR) assay using H5-specific primers and probes at your state or local public health department.
Treatment Recommendations:
- Initiation of antiviral treatment with oral oseltamivir (twice daily x 5 days) is recommended as soon as possible for any patient with confirmed, probable, or suspected infection with a novel influenza A virus.
- Treatment should be initiated even if more than 48 hours have elapsed since illness onset and regardless of illness severity (outpatients or hospitalized patients).
- For the most up to date treatment recommendations, visit the CDC’s Interim Recommendations for Prevention, Monitoring, and Public Health Investigations.
Infection Control Measures for Healthcare Settings:
- Standard, contact and airborne precautions, including the use of eye protection, are recommended when evaluating patients for infection with novel influenza A viruses.
- If an airborne infection isolation room (AIIR) is not available, isolate the patient in a private room.
- Healthcare personnel should wear recommended personal protective equipment (PPE) when providing patient care.
- For the most up to date information on recommended infection prevention and control measures, visit the CDC’s Interim Guidance for Infection Control.
Norovirus
Norovirus is the leading cause of vomiting and diarrhea, and foodborne illness in the United States. The CDC works closely with federal regulatory partners on norovirus outbreak investigations.
Symptoms:
A person usually develops symptoms 12 to 48 hours after being exposed to norovirus.
- Gastrointestinal symptoms (common): Diarrhea, vomiting, nausea, stomach pain
- Systemic symptoms (less common): Fever, headache, and body aches
Diagnostic Tests:
- Primary Testing Methods:
- Stool RT-qPCR assays are the preferred method to detect norovirus. RT-qPCR assays are very sensitive and specific.
- Enzyme Immunoassays (EIA): Detect viral antigens in stool but are less sensitive than RT-PCR. These are generally not recommended for testing single samples from sporadic cases.
Treatment Recommendations:
- Most people with norovirus illness have a self-limited course which resolves within 1 to 3 days. There is no specific treatment for norovirus. Antibiotics will not help treat norovirus infections.
- People with norovirus should watch for signs of dehydration and drink plenty of liquids to replace fluid lost from vomiting and diarrhea.
- Severe dehydration may require hospitalization for treatment with IV fluids.
Infection Control Measures for Healthcare Settings:
- Be aware that:Hand washing with soap and water is required for any contact with patients with norovirus as alcohol-based hand sanitizers do not work against norovirus.
- Noroviruses are relatively resistant to heat and can survive temperatures as high as 145°F.
- Implement policies concerning hand hygiene, patient isolation (separation of symptomatic patients), staff exclusion from work, visitor restrictions, enhanced environmental cleaning and disinfection. For additional information on Norovirus spread prevention best practices: https://www.cdc.gov/norovirus/prevention/index.html#cdc_prevention_pre-prevention-steps-and-strategies
Human Metapneumovirus (HMPV)
Although Human metapneumovirus (HMPV) is not a new virus, according to the World Health Organization, there has been a recent increase in HMPV cases in China including suggestions of hospitals being overwhelmed. HMPV can cause upper and lower respiratory disease in people of all ages, especially among young children, older adults, and people with weakened immune systems.
Although Human metapneumovirus (HMPV) is not a new virus, according to the World Health Organization, there has been a recent increase in HMPV cases in China including suggestions of hospitals being overwhelmed. HMPV can cause upper and lower respiratory disease in people of all ages, especially among young children, older adults, and people with weakened immune systems.
Symptoms:
- Symptoms commonly associated with HMPV include cough, fever, nasal congestion, and shortness of breath. Clinical symptoms of HMPV infection may progress to bronchitis or pneumonia and are similar to other viruses that cause upper and lower respiratory infections.
- The estimated incubation period is 3 to 6 days, and the median duration of illness can vary depending upon severity but is similar to other respiratory infections caused by viruses.
Diagnostic Tests:
Since HMPV is a recently recognized respiratory virus, healthcare professionals may not routinely consider or test for HMPV. However, healthcare professionals should consider HMPV testing during winter and spring, especially when HMPV is commonly circulating.
Infection with HMPV can be confirmed usually by:
- Direct detection of viral genome by nucleic acid amplification test (NAAT), and
- Direct detection of viral antigens in respiratory secretions using immunofluorescence or enzyme immunoassay.
Treatment Recommendations:
Currently, there is no specific antiviral therapy to treat HMPV and no vaccine to prevent HMPV. Medical care is supportive.
Infection Control Measures for Healthcare Settings:
- Isolate infected patients in private rooms or cohort them with others with confirmed hMPV.
- Implement standard and droplet precautions (e.g., masks, gloves, gowns).
- Enforce strict hand hygiene protocols.
- In healthcare settings, healthcare providers should follow CDC’s Isolation Precautions Guideline.
Take a Proactive Approach to Infection Prevention & Control
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References:
Centers for Disease Control and Prevention (CDC). HPAI interim recommendations for prevention and control [Internet]. Atlanta (GA): Centers for Disease Control and Prevention (US); [cited 2025 Jan 14]. Available from: https://www.cdc.gov/bird-flu/prevention/hpai-interim-recommendations.html
Centers for Disease Control and Prevention (CDC). Interim infection prevention and control recommendations for healthcare personnel during treatment of patients with suspected or confirmed novel influenza A viruses [Internet]. Atlanta (GA): Centers for Disease Control and Prevention (US); [date unknown] [cited 2025 Jan 14]. Available from: https://www.cdc.gov/bird-flu/hcp/novel-flu-infection-control/
Centers for Disease Control and Prevention (CDC). Norovirus outbreak prevention and control basics [Internet]. Atlanta (GA): Centers for Disease Control and Prevention (US); [date unknown] [cited 2025 Jan 14]. Available from: https://www.cdc.gov/norovirus/outbreak-basics/index.html
Centers for Disease Control and Prevention (CDC). Norovirus laboratory testing and diagnostics [Internet]. Atlanta (GA): Centers for Disease Control and Prevention (US); [date unknown] [cited 2025 Jan 14]. Available from: https://www.cdc.gov/norovirus/php/laboratories/index.html
Centers for Disease Control and Prevention (CDC). About norovirus [Internet]. Atlanta (GA): Centers for Disease Control and Prevention (US); [date unknown] [cited 2025 Jan 14]. Available from: https://www.cdc.gov/norovirus/about/index.html#:~:text=Treatment%20and%20recovery,they%20fight%20bacteria%2C%20not%20viruses
Lopman BA, Steele D, Kirkwood CD, Parashar UD. The vast and varied global burden of norovirus: Prospects for prevention and control. PLoS Med [Internet]. 2016 Apr [cited 2025 Jan 14];13(4):e1001999. Available from: https://pmc.ncbi.nlm.nih.gov/articles/PMC4624335/#:~:text=The%20main%20approaches%20to%20preventing,staff%20exclusion%20from%20work%2C%20visitor
World Health Organization. Trends of acute respiratory infection, including human metapneumovirus, in the Northern Hemisphere. Disease Outbreak News. 2025 Jan 7. Available from: https://www.who.int/emergencies/disease-outbreak-news/item/2025-DON550
Centers for Disease Control and Prevention (CDC). Human metapneumovirus (HMPV) [Internet]. Atlanta (GA): Centers for Disease Control and Prevention (US); [date unknown] [cited 2025 Jan 14]. Available from: https://www.cdc.gov/human-metapneumovirus/about/index.html
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