Preliminary clinical and epidemiological description of influenza A (H5N1) in Viet Nam

12 February 2004

These data have been compiled by Vietnamese clinicians, epidemiologists, and laboratory scientists involved in the treatment and investigation of cases. WHO is grateful to these authors for allowing immediate publication of their findings.

Since December 2003, an outbreak of avian influenza H5N1 has affected many countries in South-East Asia, decimating flocks of domestic poultry. To date, a limited number of human cases of H5N1 infection have been confirmed in Vietnam and Thailand. Below are tables that summarize the clinical and epidemiological features of ten confirmed cases of H5N1 infection in Vietnam.

Whilst the information about these cases may be of value to healthcare practitioners, none of the features presented here should be considered definitive, as the full spectrum of human infection by H5N1 is still being explored.

In all 10 cases, the diagnosis of influenza A H5N1 was confirmed by viral culture or reverse transcriptase PCR with H5 and N1 specific primers. Eight of the ten patients had a clear history of direct contact with poultry and there was no definitive evidence of human-to-human transmission.

Fever greater than 38°C, shortness of breath and cough are the main presenting features. All patients presented with significant lymphopenia and marked chest radiograph abnormalities. The chest X-ray abnormalities were non-specific and included diffuse, multifocal or patchy infiltrates. Some cases showed segmental or lobular consolidation with air bronchogrammes. Crackles were frequently heard on auscultation. None of the patients reported sore throat, conjunctivitis, rash or runny nose. Watery diarrhoea or loose stools was noted in around half of the cases. Eight patients died, one recovered and one remains in a critical condition.

Based on data from six of the cases, the median time between exposure and onset of illness is 3 days (range 2-4 days). In these ten patients, the mortality rate was high with death occurring a mean of 10 days after onset of illness. However, these cases were identified by alert clinicians in tertiary care hospitals and cannot be taken to be representative of the full range of illness that H5N1 may cause.