Cold temperature and consultations for respiratory and cardiovascular disease

Walter Holland

The London School of Economics and Political Science, Houghton Street, London WC2A 2AE.

Sirs—The interesting paper by Hajat and Haines1 illustrates both the advantages and disadvantages of computers. This paper, by sophisticated analysis, shows an association of temperature with consultations for respiratory disease in the primary care setting. The effect was shown to be lagged with some delay in effect. No association was shown for cardiovascular disease consultations. The data used for this sophisticated analysis was based on GP consultations in London in practices co-operating with the General Practice Research database between January 1992 and September 1995. Air pollution, temperature, relative humidity, and pollen data were obtained from a variety of sources representing the conditions in London. A highly sophisticated statistical analysis was performed in order to identify independent association. It is claimed that ‘this study seems unique, in that no previous long-term time-series analysis appears to have been undertaken to investigate the association of consultations with ambient temperature in the primary care setting’.

It is probably true that no such specific study has been done previously. The authors’ references refer to one publication in 1977, 4 in the 1980s and, 13 in the 1990s and 4 since 2000. However, no references are made to studies in the 19th century or before the era when computer indexed and abstracted publications were less common and Medline did not exist.

Computers have brought great benefits to research in epidemiology, the methodology, data handling, and information retrieval, so that research that would not have been practicable before their advent, is now possible. Another benefit is the ability to easily access references—and abstracts of indexed literature through Medline and other databases published since about 1966.

These advances, however, also have drawbacks. The ability to perform complex statistical procedures easily may tempt researchers to use inappropriate methods. Another change is that less consideration is needed to study the amount and type of data required to answer a particular problem. More importantly, however, the ability to retrieve references from on-line databases may mean that investigations performed before the initiation of these methods of retrieval are neglected.

Farr2 noted in 1885 that the most usual causes of disease in the cold months in older individuals were respiratory. The roles of weather and climate were a subject of interest to researchers in the 1920s. Young3 at the National Institute of Medical Research, first published a paper looking at mortality in children in a number of English towns between 1854 and 1919 and showed, in particular, the effect of cold in the preceding week. Russell4 showed the independent effects of fog and temperature on respiratory disease.

The Payling-Wrights5 tried to clarify the role of meteorological factors in the aetiology of infant respiratory disease and concluded that low temperature had a ‘special’ role. Various authors6–8 confirmed these findings on morbidity by examining variations in emergency admissions to Birmingham and London Hospitals, attendance at Royal Air Force sick quarters (similar to general practice) and most imaginatively by looking at prescriptions for cough medicines. These publications are noteworthy both in their use of a variety of different data sources but also because the methods of analysis were able to disentangle the effect of individual meteorological factors from seasonal effects.

Attempts to use predictions of incidence of respiratory disease from weather patterns, particular air pollution, are common in some US cities and elsewhere. The most interesting example known to me was developed by Karel Raska, one of the International Epidemiological Association’s founder members and Director of the Institute of Communicable Diseases in Prague in the 1950s and 1960s. From careful records of patient contacts with health facilities and meteorological variables in various locations in Czechoslovakia, a reasonably successful method of prediction of the likely date of onset of respiratory disease outbreaks (particularly influenza) in a town/village was developed by looking at the patterns in neighbouring areas. This information was then used to both ensure that adequate medicinal supplies were available in the town at the predicted outbreak time, but also that the leave of police, health service personnel, and elective hospital admissions were cancelled so that adequate health services were available for care of those who became ill in the outbreak. This was managed by the ‘sanitary stations’, which were abolished in the early 1990s with ‘Westernization’ of health services.

These comments are not intended to diminish Hajat and Hanes’ paper but to remind epidemiologists that their findings sometimes confirm studies done before the advent of computerized literature retrieval and that application of epidemiological data may be partly dependent on organizational/political structure.

The validity of epidemiological observations are always enhanced if the findings are observed in more than one population of ‘data source’.

References

1 Hajat S, Hanes A. Association of cold temperatures with GP consultations for respiratory and cardiovascular disease amongst the elderly. Int J Epidemiol 2002;31:825–30.[Abstract/Free Full Text]

2 Farr W. Vital Statistics. London: Stanford, 1885.

3 Young M. Influence of weather conditions on mortality from respiratory diseases. J Hyg 1924/25;23:151–73.

4 Russell WT. The relative influence of fog and low temperature. Lancet 1928;2:1128–30.

5 Payling-Wright G, Payling-Wright H. Etiological factors in bronchopneumonia amongst infants. J Hyg (Camb) 1945;44:15.[ISI]

6 Cross KW. The association of certain meteorological variables with incidence of respiratory disease in an industrial city. In: Tromp SW, Weihe WH (eds). Biometeorology II. Oxford: Pergamon Press, 1967.

7 Holland WW, Spicer CC, Wilson JMG. Influence of weather on respiratory and heart disease. Lancet 1961;ii:334.

8 Loudon RG. Weather and cough. Am Rev Respir Dis 1964;89:352.[ISI][Medline]


 

Authors’ response

S Hajat and A Haines

Sirs—We welcome Professor Holland’s comments concerning previous studies conducted in the 19th and early 20th century that were not referenced in our paper. In our case, the review of previous work was conducted by searching the Medline database, which will necessarily exclude all studies published prior to 1966. Obtaining all relevant material published prior to this date involves laborious hand-searching which would certainly be warranted for a systematic review. We agree that, where relevant, researchers should take into account investigations undertaken prior to the advent of Medline, but clearly better mechanisms for searching for earlier work are needed. We are glad to note that the results from the older studies quoted were in accordance with our own findings.





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