(Yet) another human A/H5N1 influenza case and cluster – when should Europe be concerned?

A Chinese report of a case from Jiangsu province of an almost certain son-to-father transmission of avian influenza type A/H5N1 infection was published this week, along with an accompanying comment [1,2]. The source of the 24-year-old son's infection was not established, but the authors suggest this might have occurred during a visit to a market where there was live poultry [1]. Such a way of acquiring infection (rather than direct or close contact with sick domestic poultry) has been suggested in a number of the few human cases recently detected in China [3]. However, in the case described in The Lancet, contact with poultry was not certain and, despite some retrospective investigations in the market, no H5N1 viruses were detected in birds. The son eventually died and his 52-year-old father almost certainly acquired the infection while caring for him in the hospital, as was the case in another probable human-to-human transmission in Thailand in 2004 [1,4]. In the recent Chinese cluster, the cases, their contacts and the circumstances of transmission were well investigated epidemiologically and virologically, with over ninety contacts traced. Control measures were vigorous, with contacts being treated with chemoprophylaxis, as recommended by the World Health Organization (WHO) [1,5]. The rigour of the investigation contrasts with many earlier outbreaks and is praised in the accompanying comment [2,6]. Only two of the contacts developed illness that was compatible with bird flu by symptoms and timing, but both were negative for markers of A/H5N1 infection (i.e. their illness had to be due to another cause) [1]. .