抄録
The size distribution of the local infection cluster (LIC), a group of patients reported from the same prefecture without interruption in successive weeks, was scale-free for infections that are transmitted from person to person (e.g., measles, rubella, syphilis and HIV/AIDS). For infections that never spread from person to person, the distribution was entirely random. The size distribution for measles, rubella, syphilis and HIV/AIDS could be simulated successfully by random coin tossing with probabilities that were higher for highly populated prefectures.
The size distribution of the population in the large municipalities (>120,000) as well as that of LICs were found scale free. As the number of patients per prefecture was correlated with an equation P=kNm, where m was 1.38 for syphilis, 1.63 for HIV/AIDS and 2 for measles or rubella, the frequency distribution of N1.38, N1.6 and N2, where N was population of municipalities, were compared with the frequency distributions of LIC sizes of syphilis, HIV/AIDS, measles and rubella. The frequency distribution of LICs, particularly those of measles and rubella during the large epidemic years, was close to the frequency distribution of Nm. The analysis suggested that LICs were products of stochastic events under the influence of the municipality population size.
