The World Health Organization says seven Vietnamese patients who initially tested negative for bird flu have been found to be carrying the virus after their samples were retested _ suggesting that avian influenza may be more widespread than originally believed.
All seven, who were first tested in January, have since recovered, WHO regional spokesman Peter Cordingley said Tuesday.
"There's no doubt. The WHO accepts that we are missing cases. It's quite possible that some people are falling sick and their symptoms are very light and they don't end up in hospital," he said.
"It's also possible that they have a very light viral load and Vietnamese tests may not be sensitive enough to pick it up," he said.
The WHO will wait to receive more details on the seven cases before adding them to the overall tally for Vietnam, Cordingley said.