Oct 31, 2006 (CIDRAP News) – A recent World Health Organization (WHO) report on 10 of the 12 confirmed H5N1 avian influenza cases that occurred in Turkey last winter adds to evidence that children and youth may be particularly susceptible to the infection.
The disease struck only children younger than 16, even though their parents had probably been exposed to the same probable source of infection, infected poultry, according to the Oct 27 issue of WHO's Weekly Epidemiological Record.
"To some extent, this reflects the same age distribution observed globally, where 50.5% of cases occurred among people aged <20 years, and it suggests that age-related factors may influence susceptibility to the disease," the report states.
Of the four case-patients described in the report who died, all were teenagers, while all the survivors were younger children, aged 3 to 9 years. "This reflects closely the global situation where the highest case-fatality rate (73%) has been observed in the 10-19-year age group," the article says.
Turkey was the first country outside Southeast Asia to have human cases. The WHO report discusses 10 cases that occurred in the eastern provinces of Van and Agri in late December 2005 and January 2006 and were investigated by WHO epidemiologists. The two other confirmed cases in Turkey were in other provinces, according to Mary K. Kindhauser, a WHO spokeswoman in Geneva.
A total of 21 human H5N1 cases had been reported in January on the basis of tests in a Turkish laboratory. But the WHO recognized only 12 cases that were confirmed by a reference laboratory in the United Kingdom.
At the time of the outbreak, a WHO official reported that two Turkish boys had asymptomatic H5N1 infections. But those two cases were among the nine that were never confirmed by the UK lab, Kindhauser told CIDRAP News by e-mail today.
The 10 cases covered in the report included three family clusters, one involving three cases and two involving two each. But investigators concluded that person-to-person transmission in the families was unlikely, because in each family the members fell ill within about a 2-day period, indicating they all contracted the virus from a common environmental source.
Although all three family clusters occurred near one another and within a 2-week period, "field investigations provided no evidence of human-to-human transmission between households," the report says. The families had had no interactions, and the children attended different schools.
Investigation indicated that close exposure to infected poultry was the primary risk factor for infection, the WHO says. All the patients had been exposed to backyard poultry, and at least five were known to have had contact with sick or dead poultry. The three families that had multiple cases had been sheltering their poultry indoors in late December because of severe cold.
Two patients had pet pigeons, but the birds' possible role could not be assessed because no samples were collected from pigeons in the area, the report says.
The article notes that 135 people in the two provinces had suspected cases of H5N1 and were hospitalized and treated with oseltamivir at the time, but testing ruled out all the cases.
Oct 27 WHO bulletin with report on H5N1 cases in Turkey
Jun 30, 2006, WHO bulletin with report on general epidemiology of H5N1 cases
Jan 30, 2006, WHO situation update on Turkish cases
Jan 11, 2006, CIDRAP News story "WHO says Turkish cases may yield new findings on H5N1"