[Analysis of Koch's phenomenon by BCg vaccination with the multi-puncture method in Japan]

In Japan, BCG vaccination without a prior tuberculin skin test was started in 2005. Koch's phenomenon is well known as a skin reaction that appears within a few days at the BCG vaccination site if the vaccination is given to a person infected with tuberculosis. However, little has been known regarding Koch's phenomenon in cases where BCG is administered by the multi-puncture method. All doctors who observe Koch's phenomenon are requested to provide a report to the local government, which then transfers the report to the Ministry of Health, Labour, and Welfare. The purpose of the present study was to clarify the issues and challenges regarding Koch's phenomenon in Japan.

We analyzed a total of 814 reports of Koch's phenomenon submitted between April 2005 and March 2009. The results were redefined in this study as follows. Non-specific reaction: Cases that we judged to not be infected with M. tuberculosis (not true Koch's phenomenon). This category includes cases classified as "follow up" on the report with a negative PPD result. Follow-up with positive tuberculin test: Cases that were highly suspected to be infected from a positive tuberculin test but that were followed up without treatment. This category includes cases in which treatment was recommended but was refused by the guardians. Koch's phenomenon: Cases that were treated as latent tuberculosis infection or disease. Referred to other hospital: Cases that were referred to another hospital and their final outcomes are not known. Unknown: Cases for which the final outcomes are not known due to a lack of information.

The age at vaccination from 3 to 6 months in most cases, with an average age of 4 months (124 days). Skin reactions were noticed within 3 days in most (95.6%) of the cases. No serious reactions due to Koch's phenomenon were reported. The numbers of reported cases and the rates by the number of births were quite diverse among prefectures. The results for the reports were as follows: non-specific reaction: 578 (71.1%); follow-up with positive tuberculin test: 34 (4.2%); Koch's phenomenon: 106 (13.0%); referred to other hospital: 54 (6.6 %); unknown: 44 (5.4%).

The differences in the number of reports by prefecture may partially be explained by differences in the risk of infection, but mostly by human factors such as: 1) explanation of Koch's phenomenon to guardian at the time of vaccination; 2) reaction to notification from guardian; 3) report system from doctor in charge to MHWL etc. The results showed a trend toward a steady decrease in the non-specific reaction over the 4-year period. When BCG direct vaccination was started in 2005, health professionals were not aware that a mild skin reaction at the vaccinated site could appear and then fade out within a few days without any special reason. Almost all the noted skin reactions in the first year were reported. It is now known, however, that such non-specific reactions can appear together with a negative tuberculin skin test and then fade out within a few days. The incidence of a "true" Koch's phenomenon (cases treated as LTBI or disease as well as cases diagnosed as LTBI but for which treatment was refused by guardians) was less than estimated based on the annual risk of infection. This result is probably due to the following: 1) some cases with a risk of infection do not receive the BCG; 2) a final result was not obtained in 12.0% of the cases, which must include a certain number of cases with a "true" Koch's phenomenon; 3) skin reactions were sometimes missed by guardians; 4) a proper diagnosis was not made for a suspected case; 5) the actual risk of infection in infants aged less than 4 months is less than estimated.

Accurate information regarding Koch's phenomenon should be provided to guardians as well as doctors and/or health workers in charge of BCG vaccinations.