Both the Indonesian Ministry of Health and the World Health Organisation are concerned about the cluster of human AI cases in North Sumatra, and have intensified investigation and response activities. However, while human-to-human transmission cannot be ruled out, genetic sequencing of two viruses isolated from cases in this cluster showed no evidence of genetic re-assortment or significant mutations.
The human viruses from this cluster are genetically similar to viruses isolated from poultry in North Sumatra during a previous outbreak.
An additional case of human infection with the H5N1 avian influenza virus, as part of the family cluster in the Kubu Sembelang village, has been confirmed by the health ministry. The 32-year-old man is the seventh member of an extended family to become infected with the H5N1 virus and the sixth to die from it.
Although the investigation is continuing, preliminary findings indicate that three of the confirmed cases spent the night of 29 April in a small room together with the initial case at a time when she was symptomatic and coughing frequently. These cases include the woman’s two sons and a second brother, aged 25 years, who is the sole surviving case among infected members of this family. Other infected family members lived in adjacent homes.
All confirmed cases in the cluster can be directly linked to close and prolonged exposure to a patient during a phase of severe illness. Although human-to-human transmission cannot be ruled out, the search for a possible alternative source of exposure is continuing. To date, the investigation has found no evidence of spread within the general community and no evidence that efficient human-to-human transmission has occurred. Priority is now being given to the search for additional cases of influenza-like illness in other family members, close contacts, and the general community.