Jan. 17 (Bloomberg) -- Bird flu has been mistaken by doctors for pneumonia, typhoid and at least four other diseases in Southeast Asia, causing treatment delays that might have worsened their patients' chances of survival, a study found.

Early signs of H5N1 avian-flu infection range from fever and cough to diarrhea and vomiting, researchers said in a report today in the New England Journal of Medicine. The disparate symptoms make it difficult to detect the disease clinically, with doctors in Indonesia and Thailand making a correct initial diagnosis in less than 12 percent of cases.

Treatment delays reduce survival rates in H5N1, which has killed three of every five of the 350 people known to have been infected. The median time for a patient to be seen by a doctor after symptoms began is four days, the authors said.

``There are substantial challenges to a rapid diagnosis,'' said Frederick Hayden, a doctor with World Health Organization's Global Influenza Program in Geneva and one of the study's 11 authors. ``We don't have right now an efficient, highly predictive and sensitive point-of-care diagnostic test for H5.''

Handling sick or dead poultry during the week before symptoms began is the most commonly recognized risk factor for H5N1, the authors said in a review that updated a 2005 report on clinical aspects of human avian-flu infection.

Clusters of cases with at least two linked cases have been identified in 10 nations and have accounted for about a quarter of cases, the researchers said. Limited, unsustained human-to- human transmission has probably occurred during very close, unprotected contact with a severely ill patient, they said.

Unknown Source

The source of exposure is unclear in about a quarter of cases, and exposure to the pathogen through contaminated fertilizer or infectious excreta are possible, according to the report.

Fever and pneumonia are the most common symptoms patients have at the time of their initial medical assessment, the authors said. Other clinical signs include sore throat, headache, conjunctivitis and muscle ache.

In Indonesia and Thailand, where 143 H5N1 cases have been recorded in total, some patients were initially diagnosed with tuberculosis, dengue, upper respiratory illness, leptospirosis and dizziness.

``Community acquired pneumonia is a very common syndrome, and the initial presentations are non-specific,'' Hayden said in a telephone interview yesterday. That makes it harder for doctors to suspect avian flu in patients with fever and respiratory illness, and for them to be prompted to ask patients about any possible exposure to diseased poultry, he said.

When H5N1 is suspected, it might be appropriate for doctors to collect samples and commence antiviral therapy pending results of confirmatory tests on specimens, which may take days to reach laboratories capable of running the tests, Hayden said.

Roche's Tamiflu

Roche Holding AG says its Tamiflu antiviral medicine can reduce the severity and duration of flu symptoms if taken within 48 hours of the onset of disease. Early treatment for H5N1 may improve survival, some uncontrolled studies have shown.

The H5N1 virus has spread in wild birds and domestic poultry to more than 60 countries during the past four years. World health officials fear it could spark a pandemic if it mutates to become capable of spreading from person to person by coughing and sneezing as easily as seasonal flu.

Changes in several genes are probably needed to enable the virus to adapt to humans, Hayden said. The risk of H5N1 developing into a pandemic strain hasn't diminished since it began circulating in Southeast Asia four years ago, leading to the evolution of about 10 variants, known as clades and sub- clades.

``We don't really know all the factors that could lead to the generation of a pandemic strain with H5 or one of the other avian viruses that are out there,'' he said. ``This virus is still entrenched in poultry populations in several parts of the world. There still are ongoing sporadic human cases and every one of those is an opportunity for the virus to change.''

To contact the reporter on this story: Jason Gale in Singapore at j.gale@bloomberg.net

Last Updated: January 17, 2008 06:28 EST