Doctors say they can predict how deadly a case of bird flu might be by looking at an infected person's chest x-ray.
The patients' x-rays showed distinctive disease patterns
Their findings are based on their experience from 14 people with bird flu treated at the Ho Chi Minh City Hospital in Vietnam.
The patients' x-rays showed distinctive disease patterns.
However, these patterns do vary from patient to patient and could indicate what treatment each needs, radiologists at the University of Oxford said.
Those with more severe lung damage might need more aggressive treatment planning to improve their chance of survival, for example.
Dr Nagmi Qureshi, a radiologist expert at the University of Oxford in the UK, who studied the 98 chest x-rays from the 14 patients, said: "The most common abnormality we found was multifocal consolidation, which usually represents pus and infection in patients with fever and a cough.
"We also discovered that the severity of these findings turned out to be a good predictor of patient mortality."
Of the 14 patients studied, nine died and five survived.
Three of the five patients who survived underwent more lung imaging, with computed tomography (CT), after discharge from the hospital.
Distinct lung damage
The CT images showed that even though the patients' respiratory symptoms had abated, the abnormal appearance of the lungs persisted, suggesting the infection had scarred the lungs.
Dr Qureshi told a meeting of the Radiological Society of North America that the bird flu findings were similar to those seen in patients with severe acute respiratory syndrome (SARS).
"However, additional abnormalities we discovered in avian flu patients, including fluid in the space surrounding the lungs, enlarged lymph nodes and cavities forming in the lung tissue-were absent in patients with SARS."
Symptoms of avian flu in humans have ranged from ordinary flu-like symptoms - fever, cough, sore throat and muscle aches - to eye infections, pneumonia, severe respiratory diseases and other severe and life-threatening complications.
Professor Peter Openshaw, head of respiratory infections at the National Heart and Lung Institute at Imperial College London, said: "It is very helpful in building up a picture of how bird flu is able to damage the lungs and how it may cause such a high mortality rate.
"But clearly, it is just part of building that picture. What we still really need to know is what are the fundamental reasons for the severity of the disease in avian flu when this infects humans."
Lessons to learn
Luckily, few humans have caught bird flu so far because the virus has not mutated into a form that is readily transmitted from person to person.
However, this also means that there are relatively few examples for doctors to learn from, said Professor Openshaw.
"We need to know how we can protect people better by making improved vaccines.
"It's impossible to know how much of a risk it is going to be to people when it has mutated until it has mutated."
"We do not know what the best treatments are," he added.
In the people who have caught bird flu so far, the main treatments have been to manage or prevent any complications, such as breathing problems.
"It's clear that antivirals should be used at the early stage and that is very effective at getting rid of the virus. But it doesn't necessarily prevent the complications of respiratory failure for example.
"It seems to be a cascade of immune events that are triggered by the virus even though the virus has been eliminated.
"And we don't know whether steroids are beneficial or harmful. It is possible that a lot of the long-term side effects seen in the SARS outbreak were actually due to steroids and that they could have been avoided."