Since yesterday, the Ministry of Public Health in
These new cases bring the total in
Investigation of possible human-to-human transmission in a family cluster.
The most recent cases are part of a family cluster of four cases under investigation to determine whether human-to-human transmission may have occurred. Immediate investigation of any possible human-to-human transmission is always needed to determine whether transmission has been efficient and sustained. Such a situation would be cause for alarm, as it might signal the start of an influenza pandemic. Inefficient, limited human-to-human transmission may occur on rare occasions and is in line with what is known, from epidemiological and laboratory investigations, about the possible behavior of the H5N1 virus.
The initial case in the family cluster was an 11-year-old girl who died of pneumonia on September 8. Thai authorities regard her as a probable case of H5N1; laboratory confirmation is not possible as no specimens from this patient are available for testing. The girl, who lived in the
The girls 26-year-old mother, whose infection is also now confirmed, resided in the
Thai officials have concluded that the mother could have acquired the infection either from some environmental source or while caring for her daughter, and that this represents a probable case of human-to-human transmission.
The family cluster also includes the six year-old son of the aunt of the initial case. He was hospitalized but is recovering, and samples are being tested.
Surveillance for additional cases, among health workers and in the wider community, has been greatly intensified in the province, and hospitals nationwide have been placed on heightened alert for further cases.
While the investigation of this family cluster provides evidence that human-to-human transmission may have occurred, evidence to date indicates that transmission of the virus among humans has been limited to family members and that no wider transmission in the community has occurred. Continued vigilance is needed to determine whether the epidemiological situation in humans remains stable.
Clinical samples taken from cases in the family cluster were immediately shared with a laboratory in the WHO Global Influenza Surveillance Network. Virus isolated from these samples will undergo genetic and antigenic analysis to determine whether the virus has evolved and, more specifically, whether it has acquired genes that allow improved transmissibility among humans.