History and exam
Key diagnostic factors
common
cough
Present in most hospitalized patients and can be dry or productive. Hemoptysis was reported in 25% patients in one series.
influenza-like illness
Nonspecific symptoms that are often associated with influenza including cough, fever, headache, myalgia, and fatigue have been reported in some clinically mild cases and as the initial symptoms prior to progression to lower respiratory tract disease. Sore throat and rhinorrhea appear to be less likely.
dyspnea
Present in over half of hospitalized patients in a large published series.
fever
Usually temperature >100.4°F (>38°C) occurs early in the course of illness and may persist, especially with severe illness, but an absence of pyrexia does not exclude the possibility of infection.
decreased breath sounds
Frequency unknown, but common auscultatory finding in severe illness caused by other influenza A viruses. Signals decreased air movement through a part of the lung or lungs, and could indicate pulmonary consolidation, atelectasis, effusion, or acute respiratory distress syndrome.
tachypnea
Frequency unknown, but common finding in severe illness caused by other influenza A viruses.
Other diagnostic factors
uncommon
vomiting, diarrhea
Nonspecific primary gastrointestinal symptoms have been reported in some A(H7N9) virus-infected patients.
altered mental status
Nonspecific neurologic symptoms have been reported.
Risk factors
strong
environmental exposure to Asian lineage A(H7N9) virus
Many (but not all) patients with Asian lineage A(H7N9) virus infection report having visited or worked at a live poultry market in China. Some low-pathogenic avian influenza (LPAI) A(H7N9) virus-infected patients reported having direct or close contact with backyard poultry in rural areas of China. Most animal exposures involved poultry, but exposures to other birds and mammals have been reported.[7] Asian lineage A(H7N9) virus has been detected in chickens, ducks, and pigeons, but not in pigs. Asian lineage A(H7N9) virus RNA has been detected in goose meat and also in sewage obtained from a wet market.
weak
close contact with infected humans
Approximately 40 case clusters of Asian lineage A(H7N9) virus infection have been reported since 2013, with most of the clusters containing no more than two individuals. Epidemiologic investigations of family clusters suggest that most cases of Asian lineage A(H7N9) virus infection had poultry exposures. However, close and prolonged unprotected exposure, including providing basic care to an index case, is the most likely explanation for limited, unsustained human-to-human transmission in some clusters; this has been reported after prolonged unprotected exposures in blood-related family members and in unrelated people, including nosocomial transmission (patient-to-healthcare worker, and patient-to-patient). The risk of human-to-human A(H7N9) virus transmission was similar during 2013 to 2017 and remains low.[11]
laboratory work with A(H7N9) virus
Transmission of Asian lineage A(H7N9) virus to laboratory workers is not known to have occurred when appropriate laboratory health and safety measures have been followed.
A small serologic survey of laboratory workers exposed to highly pathogenic avian influenza (HPAI) A(H5N1) virus with incomplete personal protective equipment use and adherence to biosafety precautions demonstrated no serologic evidence of prior HPAI A(H5N1) virus infection.[106]
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