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January 10, 2006
Tuberculosis and Infectious Diseases
Control Division,  Health Service Bureau
Director: Tsukahara
Person in charge: Kanari (Extension 4609)

Regarding the results of avian influenza antibody tests in Ibaraki and Saitama prefectures

1    Overview

Since June 2005, physical examinations and virus tests were conducted to evaluate the presence of infection in chicken farm employees etc. (workers at chicken farms and their families who had close contact with poultry) and some health workers in Ibaraki and Saitama prefectures, where A/H5N2 avian influenza (low virulent ) had been confirmed. However, no cases showed influenza-like symptoms, and all the results of virus genetic tests using the PCR test, were negative.

In addition, serum neutralizing antibody tests were conducted to verify present or past infection, and an interim report has been created.  Serum antibody tests were conducted in 31 Ibaraki prefecture government officials who had never engaged in killing poultry etc., as the control group.
2 Results of serum antibody tests

Serum antibody tests were conducted as soon as infection of poultry was confirmed (first antibody test) and approximately one month later, by collecting blood samples (second test).

The following table shows the results.  Since the criteria for evaluating antibodies against the H5N2 influenza virus with attenuated virulence have not been established, general evaluation taking the epidemiological background into consideration is necessary.

   First antibody test Second antibody test Number of subjects with increased antibody value
(four-fold and over)
Number of subjects Number of positive cases* Number of subjects Number of positive cases*
Employees at chicken farms etc. 319 44 231 34 15
Health workers 34 5 33 1 0
(Antibody tests completed by the end of 2005)

*    In this study, since no cases with a neutralizing serum antibody value over 40 were found among the 31 control subjects, an antibody value of 40 and over was defined as the tentative criterion for a positive result.  It should be noted that this criterion is only tentative.

3 Discussion

There were 15 cases with an increase in antibody value of more than 4-fold from the first to the second test.  At present it is speculated that they were infected shortly before the first blood collection.  Concerning the other 62 positive cases, the time of infection cannot be specified, but it seems possible that infection could have happened at any time point.

At infected chicken farms there were no preventive measures against infection for a long time before infection of poultry was confirmed, so it is considered that infection occurred due to exposure to the virus through contact with poultry or the contaminated environment.

On the one hand, concerning those health workers with a positive antibody value at the first antibody test, the antibody value was reduced at the second test. It suggests that infection was not due to infection control activities in these poultry farms.

Since avian influenza infection is not persistent, and the incubation period from infection to onset of the disease is one to three days, there is no risk antibody positive cases will contract the disease in the future.  In addition, since infected persons usually discharge the virus only for one week, it is not possible that they will infect others hereafter.
4 Significance of the survey

1)    At present, it is speculated that humans may be infected with the H5N2 avian influenza with attenuated virulence, which has been found in poultry in Ibaraki, although its pathogenicity in humans has not been confirmed.
2) Since the current H5N2 avian influenza virus has low virulence in poultry, and it does not show clear clinical symptoms, preventive measures such as wearing a mask when working, and washing hands, etc. should be followed strictly by all  people who come into contact with poultry until transmission of the virus is brought under complete control.
3) Patients with regular influenza should respond appropriately, for example by refraining from working at chicken farms, to avoid combined infection with avian influenza.

Dated today, the Ministry of Health, Labour and Welfare issues a notification, based on the above outline to the Ministry of Agriculture, Forestry and Fisheries and the prefectural health departments.

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