Avian Influenza (4): Symptoms

Now, we will address the clinical features.

The clinical spectrum of influenza A (H5N1) in humans is based on descriptions of hospitalized patients. The frequencies of milder illnesses, subclinical infections, and atypical presentations (e.g. encephalopathy and gastroenteritis) have not been determined, but case reports indicate that each of these do occur. Most patients have been previously healthy young children or adults before onset. This maybe due to the incubation period of H5N1 may be longer than for other known human influenzas. In 1997, most cases occurred within 2-4 days after exposure, sometimes up 8 days later. The case-to-case intervals in household clusters have generally been 2-5 days (max 8-17 days), possibly owing to unrecognized exposure.

Most patients have initial symptoms of high fever (typically a temperature of more than 38°C) and some present with an influenza-like illness with lower respiratory tract symptoms. Conjunctivitis is rare with H5N1 infections, unlike patients infected with avian influenza A (H7) viruses.

Early symptoms reported in some patients are: 

diarrhoea (watery without blood)
vomiting
inflammatory changes
abdominal pain
pleuritic pain
bleeding from the nose and gums

These symptoms may preced precede respiratory manifestations by up to one week. However, patients have presented with an encephalopathic illness and diarrhoea without apparent respiratory symptoms.

In the next section we will assess the radiological appearances and diagnostic methods.

AMH.