S. Korea Confirms 10 Human Infections of Avian Influenza H5N1 from 2003 and 2006

[Gert van der Hoek]

Asymptomatic Carriers of AI Confirmed in S. Korea

2014-02-04

South Korea was found to have seen cases of human infection with avian influenza.

The Korea Centers for Disease Control and Prevention confirmed that ten people who had participated in culling birds during the outbreaks of bird flu in 2003 and 2006 had antibodies for the H5N1 strain of avian influenza.

The fact that antibodies were found in the ten people signifies that the ten people had been infected with the virus.

The disease control agency categorized the ten people as “asymptomatic carriers,” as they displayed no symptoms.

The agency said that it had announced before that there were no human infection cases as asymptomatic carriers are not regarded as patients under the World Health Organization standards.

KBS

[Emily]

Re: S. Korea Confirms 10 Human Infections of Avian Influenza H5N1 from 2003 and 2006

I hope we'll learn more about the reasoning behind this confirmation.

http://wwwnc.cdc.gov/eid/article/18/...31_article.htm

Kwon D, Lee J-Y, Choi W, Choi J-H, Chung Y-S, Lee N-J, et al. Avian influenza A (H5N1) virus antibodies in poultry cullers, South Korea, 2003?2004. Emerg Infect Dis [serial on the Internet]. 2012 Jun [date cited]. http://dx.doi.org/10.3201/eid1806.111631

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Conclusions

By identifying only 9 seropositive cases among 2,512 persons, we determined that the risk for poultry-to-human transmission of the influenza (H5N1) virus is small. Other studies have also shown low frequencies of poultry-to-human (H5N1) virus transmission. In provinces in Thailand, blood samples were collected from 322 poultry farmers 6 months after confirmation of influenza (H5N1) virus outbreaks; all antibody titers were negative (5). Two studies of villagers in Cambodia who had frequent and direct contact with poultry with confirmed and suspected influenza (H5N1) virus infection found low frequency of virus transmission from poultry to humans (6,7). Similarly, a study in Nigeria also found negative results for antibodies against influenza (H5N1) virus among 295 poultry workers (8).

Because our study was conducted as a public health response, it has the following limitations. We were unable to systematically assess symptoms, extent of exposure, compliance with PPE use, and taking of oseltamivir. It is not clear if the participants were exposed to birds with confirmed or suspected influenza (H5N1) virus or whether they wore PPE properly when culling. Because the outbreak created an emergency situation and this study had not been designed before the outbreak, epidemiologic data were limited. And because we had insufficient serum for adsorption assays, we cannot exclude the possibility of cross-reactivity with circulating antibodies resulting from seasonal influenza vaccination or previous infection with human influenza virus. In 2004, among 83 Vietnam hospital employees who were exposed to 4 patients with confirmed and 1 patient with probable influenza (H5N1) virus infection, a positive antibody titer against influenza (H5N1) virus and cross-reacting antibodies against influenza (H1N1) virus was found on MN assay for 1 employee (12). Because our study was not a case?control study, we could not identify risk factors for transmission.

Regardless of these limitations, our study shows serologic evidence of influenza (H5N1) virus transmission among groups at high risk for poultry-to-human transmission (i.e., exposed to poultry during 2003−2004 outbreaks in South Korea). However, we also found additional proof that the frequency of poultry-to-human influenza (H5N1) virus transmission is low.

All persons who participated in the culling operations were equipped with World Health Organization (WHO)?recommended personal protective equipment (PPE) (4). To prevent the possibility of mixed infection with human and avian influenza viruses, previously nonvaccinated participants were vaccinated with a seasonal influenza vaccine and given oseltamivir as an additional prophylactic measure.

All those with influenza (H5N1)?positive results were male, median age was 32.5 years (range 22?48 years), and all had participated in culling during the outbreaks (Table 2). None of the other poultry farm workers had seropositive results.

That would make me lean toward thinking that the seropositive results were due to cross-reactivity with circulating antibodies resulting from seasonal influenza vaccination of the culling workers.