The method of transmission of epidemic influenza: further evidence from archival mortality data.

Evidence for influenza-associated excess mortality in the three centuries before the 20th has been sought from parish burial registers in Cumbria, Devon, Dyfed, East Anglia, Gloucestershire and Northumbria, compared with inter-epidemic years. Most of the registers showed excess of burials concordant with eight historic influenza epidemics. Comparison of the dates of these epidemics, deduced from the burials data in different areas, showed a rate of spread difficult to reconcile with direct person-to-person spread of influenza from the sick. An alternative explanation based on development of latency of the virus in the sick person and subsequent seasonal reactivation is discussed.

Effect of influenza epidemics on Australian mortality.

The effect of influenza epidemics on all major causes of death has been examined. The results showed an increase in total mortality, and a fall in life expectancy, during epidemic years. Using the 1974 epidemic as an example, an increase in mortality was found in all age groups, with the greatest percentage in increases occurring in the very young and the very old. For all ages combined, the greatest percentage increases in mortality were for respiratory diseases, while the greatest absolute increases in mortality were for cardiovascular diseases, especially ischaemic heart disease. A thrombotic mechanism is suggested to explain the increase in mortality from cardiovascular diseases.

Causes of mortality in a subarctic settlement (York Factory, Man.), 1714-1946.

A 250-year retrospective mortality study of York Factory, on the shores of Hudson Bay, was undertaken. The daily journals of the Hudson's Bay Company and the records of the Anglican Church of Canada were the principal sources examined. From 1714 to 1801 the death rate among the Europeans was 0.015 per year, about 10 times today's level but in line with American figures of the period. The high mobility of the population during the 19th century precluded statistical assessment. In the first half of the 20th century the Europeans left; among the Cree Indians who stayed 316 out of 401 deaths were caused by infection. As in the preceding eras, tuberculosis and influenza, sometimes in epidemic form, were the most commonly diagnosed diseases. The settlement's overall mortality rate in those last 45 years was 0.03 per year, triple that for the rest of Canada in 1932.

A study of excess mortality during influenza epidemics in the United States, 1968-1976.

The effect of epidemics of influenza A on mortality in the United States was assessed by studying the monthly numbers of deaths during the years 1968-1976. Deaths from all causes at all ages and among persons aged 65 and over, and also deaths from acute respiratory diseases, and from cardiovascular causes were studied. Deaths from acute respiratory diseases were closely correlated with those from influenza and were taken to be an indication of the severity of influenza outbreaks. This indicator combined with a regression function expressing seasonal variation and secular trend was used to predict total mortality, cardiovascular mortality, and deaths among persons aged 65 and over. In each case the predictions proved to be reasonably close to the observed numbers of deaths. Excess mortality from all causes above that expected from seasonal variation occurred principally in three periods during the eight years of study: 1968-1969, 1972-1973, and 1975-1976, each of which coincided with an epidemic of influenza A of the H3N2 subtype. Similar excesses were seen among persons aged 65 and over and in cardiovascular deaths during the two earlier periods. It is concluded that excess mortality occurred during at least three of the major outbreaks of influenza during the period 1968-1976. This points to the need of studying the effectiveness of immunization in preventing the disease.

Seasonality of plague in early modern Europe: Swiss epidemic of 1628--1630.

The course of plague is markedly influenced by seasonal factors. A quantitative estimate of its seasonal distribution was made from parish death books of 38 communities in a small, diversified area of Switzerland for the epidemic period of 1628--1630. The temporal distribution of outbreaks was bimodal with maximal mortalities in the autumn-early winter seasons of two successive years. Of 43 peaks of mortality, 39 occurred between September and January; November was the month of highest frequency. Colder weather exerted a gradual limiting influence, but late-blooming community outbreaks continued at a high or maximal level as late as January. Evidence is presented that the temporal distribution of outbreaks affected the persistence of plague in the region. The seasonality of plague in Switzerland contrasts with the pattern in Great Britain, where midsummer epidemics prevailed.