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CDPH Novel Influenza A (H5N1 and H7N9) Information Webpage

CDPH conducts surveillance for novel influenza viruses that have the potential to become pandemic viruses and cause severe morbidity and mortality.  Influenza viruses constantly change. For some influenza viruses that circulate in poultry and swine, certain mutations may allow the viruses to acquire the ability to spread easily and sustainably among humans.  This could trigger a global outbreak of disease (pandemic).  Two avian influenza viruses are currently of particular concern.

Highly pathogenic avian influenza A (H5N1) virus – referred to as HPAI H5N1 and sometimes shortened to H5N1 – is a virus that occurs mainly in birds, is highly contagious among birds, and can be deadly to them, especially domestic poultry. Though relatively rare, sporadic human infections with this virus have occurred and caused serious illness and death.  HPAI H5N1 was first described in 2003 and has now spread to several countries where it is considered endemic in poultry.  Human infections with HPAI H5N1 have appeared to have resulted from close exposure to infected poultry or a contaminated environment. The most common clinical syndrome is fever and cough which in some patients progresses rapidly to several viral pneumonia with shortness of breath, difficulty breathing, and hypoxia.  Frequent complications include respiratory failure, acute respiratory distress syndrome (ARDS), multi-organ failure, and death.  No evidence of sustained person-to-person spread of HPAI H5N1 has been found, though some evidence points to limited person-to-person spread in rare circumstances.  In January 2014, Canada reported a fatal case of human infection with avian influenza A (H5N1) in a patient who had recently traveled to Beijing, China. This is the first human H5N1 case reported in North or South America.  To date, there have not been any reports of HPAI H5N1 virus infections among wild birds, poultry, or other animals or humans in the United States.

Avian influenza A (H7N9) [H7N9] virus infection of humans was first reported in April 2013 in China.  Most of these human infections are believed to result from exposure to infected poultry or contaminated environments, as H7N9 viruses have also been found in poultry in China. While some mild illnesses has been described, most patients have had severe respiratory illness, with about one-third resulting in death. H7N9 infection in poultry is difficult to detect as infected birds may often be mildly ill or asymptomatic.  No evidence of sustained person-to-person spread of H7N9 has been found, though some evidence points to limited person-to-person spread in rare circumstances. H7N9 has also been detected in travelers from H7N9-affected countries.  No cases in either people or poultry have been reported in the United States.

California is at high risk for importation of a novel influenza virus given its large population and number of international ports of entry.  CDPH encourages health care providers to be alert and report patients who meet the following clinical case definition and exposure criteria to their local health departments: 

Clinical Illness Criteria:

·         Patients with new-onset severe acute respiratory infection requiring hospitalization AND;

·         Patients for whom no alternative infectious etiology is identified.

Exposure Criteria:

·         Recent travel (within ≤ 10 days of illness onset) to a country where human cases of H7N9 have been detected; OR

·         Recent close contact (within ≤ 10 days of illness onset) with a confirmed case of human infection with H7N9 virus.

·         History of working with a live novel influenza virus in a laboratory.

At this time, all suspect cases of novel influenza A virus should be tested by a California public health laboratory.

For more information on testing patients for novel influenza A infection, please see the CDC guidance at: http://www.cdc.gov/flu/avianflu/h7n9/specimen-collection.htm.

*In contrast to the CDPH clinical case definition, current CDC guidances recommend testing of all travelers from areas where novel virus has been detected, regardless of severity of illness (http://www.cdc.gov/coronavirus/mers/case-def.html).  At their discretion, local health departments may choose to consider testing of outpatient, non-hospitalized cases who otherwise meet the clinical case definition and exposure criteria.  Local health departments are encouraged to contact CDPH at (510) 620-3737 or (510) 231-6861 for consultation.


General Information
Last modified on: 10/29/2015 1:58 PM