Study suggests preschool kids, non-elderly adults most susceptible to H1N1
A serologic survey from British Columbia suggests that preschool children and working-age adults are the groups most susceptible to the pandemic 2009 H1N1 influenza virus, by far the most common strain in North America so far this flu season.
The survey, conducted in the Vancouver, B.C., area last spring, showed that fewer than 20% of children under 5 years old had H1N1 antibody titers suggesting protection, according to findings presented on ProMED-mail by Danuta Skowronski, MD, of the British Columbia Centre for Disease Control.
Protective antibody levels (titers of 40 or higher) were found in 45% to 50% of adults of ages 20 to 39 years and in 35% to 40% of those ages 40 to 69, Skowronski wrote. Seroprotection was most prevalent—60% or higher—in school-age children and in adults 70 and older.
"Our age-related observations for the spring 2013 suggest pre-school children and young or middle-aged adults are currently the most susceptible" to 2009 H1N1 infection, she wrote.
She noted that more than 80% of flu viruses subtyped in British Columbia this season have been 2009 H1N1, and serious outcomes have been reported in some young and middle-aged adults. This has come amid "a striking absence of other more typical early warning signals of influenza circulation such as school or long-term care facility (LTCF) outbreaks."
The seroprotection findings "may help put current surveillance trends into context," Skowronski wrote. "Given the greater seroprotection identified in school children and the elderly, it could be speculated that A(H1N1)pdm09 is propagating more surreptitiously through adult contact networks without the usual school or LTCF outbreaks as expected surveillance signals and with dampened activity levels overall at the community level."
The overall prevalence of H1N1 antibodies found in the serologic survey approached 50%, which was similar to findings in the spring of 2010, following the 2009 pandemic, but age-specific findings were slightly different, she reported.
Jan 1 ProMED-mail post
Related Dec 20 CIDRAP News story
H9N2 confirmed in Chinese child
Health officials in China yesterday announced an H9N2 avian influenza infection in a 7-year-old boy from Hunan province, marking the second H9N2 case reported in China this week.
Hong Kong's Centre for Health Protection (CHP) said today that the boy, from the city of Yongzhou, had a fever and runny nose on Nov 19 and was treated at a hospital the next day. The CHP said Chinese health officials confirmed the case yesterday and reported that the boy had a history of contact with poultry.
Human infections with H9N2 influenza are sporadically reported and usually cause mild respiratory symptoms. On Dec 30 the CHP reported the virus in an 86-year-old Hong Kong man who currently lives in Shenzhen, across the border from Hong Kong. The man's H9N2 infection was the first reported in the area in 4 years.
Jan 2 CHP statement
Dec 30 CIDRAP News item "Hong Kong reports H9N2 flu case"