T.W. Anderson

Does screening by " Pap " smears help prevent cervical cancer? A case-control study.

The Papanicolaou (Pap)-smear history of 212 cases of invasive cervical cancer was compared with that of 1060 age-matched controls drawn from neighbours. In the 5 years before the year of diagnosis 32% of the cases had been screened by Pap smear, compared with 56% of the controls. This difference was statistically highly significant (p less than 0.0001) and indicated a relative risk of invasive cancer of 2.7 in women who had not been screened by Pap smear, compared with those who had. Differences in Pap-smear history between cases and controls persisted when the data were stratified by age, income, education, marital history, smoking habit, employment status, and access to medical care. These results support the belief that the Pap smear is an effective screening procedure for invasive cervical cancer.

Sudden death and ischemic heart disease. Correlation with hardness of local water supply.

Abstract Investigations conducted in several parts of the world have shown that residents of soft-water areas have a higher death rate from ischemic heart disease than residents of hard-water areas. The same pattern appears to exist in Ontario, but when deaths are divided into sudden and nonsudden (on the basis of whether or not the death certificate was signed by a coroner), the higher death rate in the soft-water areas is found to be due entirely to an excess of sudden deaths. This finding suggests that the correlation between cardiac mortality and water hardness may be the result of an increased susceptibility to lethal arrhythmias among residents of soft-water areas.

COLD WEATHER AND MYOCARDIAL INFARCTION

Abstract The marked seasonal fluctuation in ischaemic heart-disease (I.H.D.) mortality in England and Wales has been attributed to a direct effect of environmental temperature on liability to myocardial infarction. If this explanation is correct, then Ontario, with its warmer summers and colder winters, should have an even more pronounced seasonal fluctuation in I.H.D. mortality. Similarly northern Ontario, which experiences very severe winters, should show a more marked seasonal fluctuation than the relatively mild southern part of the Province. In fact, the seasonal fluctuation in I.H.D. mortality in Ontario is substantially less than that in England and Wales, and there is little or no difference in the magnitude of the fluctuation in northern and southern Ontario. Evidence discounts the possibility that the smaller seasonal swing in Ontario is due to differences in diagnostic fashion, the relative youth of the population, or the protective effect of universal central heating. It is suggested that most, if not all, of the seasonal fluctuation in I.H.D. mortality is due, not to a direct effect of environmental temperature on the tendency to myocardial infarction, but to the very marked seasonal fluctuation in serious respiratory disease. Mortality data from Australia and Denmark, together with an analysis of seasonal variation in sudden death in Ontario, support this explanation.

A CRITICAL REAPPRAISAL OF THE EPIDEMIOLOGY OF CEREBROVASCULAR DISEASE

Abstract Estimates of age-specific death-rates from cerebrovascular disease have been prepared by examining a sample of Ontario death certificates from every tenth year between 1901 and 1961. During this time among persons aged 45-74 years there was little change in the total death-rate from cerebrovascular disease, and the proportion of males and females remained approximately equal. According to the diagnoses appearing on death certificates, between 1901 and 1961 the proportion of cerebrovascular deaths due to thrombosis rose from 2% to 22%, while the proportion due to haemorrhage fell from 27% in 1901 to 61% in 1931, and to 36% in 1961. This changing pattern of cerebral haemorrhage and thrombosis is similar to that reported from other parts of the world, but since it is often difficult to distinguish clinically between cerebral thrombosis and cerebral haemorrhage, it is open to question whether these trends reflect true changes in aetiology. The validity of these trends has been tested by examining for evidence of corresponding changes in the reported interval between onset of illness and death. The absence of such changes indicates that there has been no significant alteration in the incidence of cerebral haemorrhage or thrombosis during the past 60 years. A comparison of necropsy findings in patients who died from cerebrovascular lesions in the Toronto General Hospital during 1930-36 and 1960-62 provides additional evidence that the incidence of these conditions has remained relatively constant during the past three decades. These findings suggest that there may have been little change in the prevalence of atherosclerosis during the past sixty years.