Mortality in the 1957-58 Influenza Epidemic

Abstract

OU ITBREAKS of A-prime influenza had scarcely subsided in the United States and Europe late in the spring of 1957 when it was reported that an epidemic of influenza had broken out in Hong Kong about the first part of April. Confirmation that a new strain of type A infl-uenza virus, now referred to as the Asian strain, was causing the disease was obtained by the third week of May. The disease was reported to be mild and to have a low mortality, although reports from Manila indicated that the number of deaths from all causes was higher than usual in that city. Introduction of the new strain of virus into the United States from the Far East probably took place by the last of May 1957, and the first outbreak identified as due to Asian influenza began early in June in Newport, R. I. During, the summer, the disease in the United States was characterized by a series of localized epidemics, some of them interrelated, in closed groups of teen-age children and young adults. Undoubtedly, dispersal of members of some affected groups to various parts of the country served to seed the population extensively before the end of the summer. During this period, deaths attributed to influenza were few, and the mortality rate from influenza and pneumonia was not higher than expected. One communitywide epidemic of influenza occurred in Louisiana late in August. In September, when schools in most parts of the country opened, explosive epidemics began first in high schools and colleges and immediately thereafter in elementary school populations and in preschool children. Incidence in adults was not excessively high. The peak of the epidemic was reached in the thifd week of October, after which incidence declined throughout November and December. During January, February, and March, the occurrence of influenza was characterized by numerous localized outbreaks, principally in school and other institutional populations. During the height of the epidemic in October, respiratory disease rates as estimated by the U. S. National Health Survey were about 111 per 1,000 persons per week in the age group 5 to 19 years, 28 per 1,000 under 5 years, 16 per 1,000 in the group aged 20 to 64 years, and about 9 per 1,000 in persons 65 years of age and over. Data from two sources show the effect of the influenza epidemic on mortality: the numbers of deaths credited to influenza and pneumonia in 108 large cities, reported weekly to the National Office of Vital Statistics, Public Health Service; and the Current Mortality Sample, consisting of a 10 percentsample of all death certificates filed in State departments of health, copies of which are sent each month to the National Office of Vital Statistics (1, 2). These data are provisional; final figures will be available in early 1959.