"Although human-to-human transmission cannot be ruled out, the search for a possible alternative source of exposure is continuing," the World Health Organisation said in statement yesterday.
But it also said that all confirmed cases in the family cluster could be directly linked to prolonged exposure to a patient during the phase of severe illness.
The six were identified as member of an extended family and the WHO said a seventh member was infected with H5N1 virus. However, the agency also reassured that the virus has not mutated to a more deadly form.
To date, WHO said, the investigation has found no evidence of spread within the general community and no proof that efficient human-to-human transmission has occurred.
Despite highly cautious statement by the agency, the largest cluster of deaths in a family since the virus was identified evoked fears of the possibility that the virus might be evolving into a form could result in human-to-human infection.
Full genetic sequencing of two viruses isolated from cases in the Indonesian family cluster, has been completed by WHO H5 reference laboratories in Hong Kong and the USA.
Sequencing of all eight gene segments found no evidence of genetic reassortment with human or pig influenza viruses and no evidence of significant mutations. The viruses showed no mutations associated with resistance to the neuraminidase inhibitors, including oseltamivir (Tamiflu), it added.
Source: PTI News