Seasonal variation in the month of first visit for atopic dermatitis patients

Abstract

The total number of new attendant patients diagnosed as having atopic dermatitis at our dermatology out-patient clinic during the 7 year period from 1989 to 1995 was 10 156. Patients from each year during this period were divided into eight age groups. The birth month and the month of first visit for each age group was obtained in average of 7 years. Only for subjects aged <1 year was there a definite tendency for higher birth numbers in autumn and lower birth numbers in spring. The percent birth rate for subjects <1 year of age was significantly higher in October and November and significantly lower in March and May in comparison with the expected percent birth rates calculated on the basis of birth months of the Japanese population. Similarly, patients aged <1 year, 1-2 and 3-5 years showed a tendency for higher numbers of first visits in spring and, in addition, patients aged <1 year showed a tendency for smaller numbers of first visits in summer. At school and college ages, between 6 and 20 years of age, a steep increase of first visits was observed in March and a smaller increase of first visits was observed between July and August. We investigated whether the distribution of birth month for subjects aged <1 year was statistically significant. The percent first visiting month was significantly higher in March and April and lower between July and October in comparison with the expected percentage first visiting month. We speculated that the uneven distribution of birth month was a reflection of a more marked distortion observed in the distribution of the month of first visit. The mean age at first visit (6.24 months) explains the difference between first visiting month and birth month. There were no definite social reasons for the increase in the number of first visits in spring for subjects aged <1 year. Therefore, the uneven distribution of the month of first visit for subjects aged <1 year could probably be the result of climatic effects.