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During the 17 years period from 1967 to 1983 a total number of 1322 children were hospitalized for infectious croup (stenosing laryngotracheitis) at the Children's Hospital in Bochum. The epidemiology of this disease, especially the yearly and seasonal incidence as well as clinical symptoms were analyzed. For this purpose at least 18 data were obtained from each patient and processed by computer using an especially elaborated FORTRAN IV program. The main incidence of infectious croup was in fall and winter, with a peak in September and October. The symptoms began usually at nighttime and boys were affected 2.5 times more frequently than girls. The risk of disease was highest in the second year of life and decreased sharply with the begin of school age. Sixteen per cent of the children had recurrent attacks of stenosing laryngotracheitis. The main therapeutic procedures were listed and discussed. Besides air humidification, sufficient application of liquids and steroids in serious cases, racemic epinephrine given by mask and positive pressure ventilation has been demonstrated to be very effective. While the viral etiology of this disease has been well established possibilities in which way meteorological and environmental factors might contribute to the manifestation of this disease are discussed. This problem can be solved only by prospective investigations. No statistically relevant increase in the number of cases of stenosing laryngotracheitis during recent years can be found in the presented results.

Results of a recently published study over a test period of 18 years showed no relationship between croup incidence of hospitalized children and SO2 levels measured in the city of Bochum. In the following study 642 hospitalized children with stenosing laryngotracheitis were examined for a possible time-dependent relationship between croup incidence and NO2, NO- and dust immission levels measured in the city of Bochum (approx. 1000 000 readings). Evaluation of a 6-year period yielded a decrease of croup patients for the lower NO2 concentration range and a statistical increase of croup cases during days with higher NO2 concentrations. However no cause-effect relationship between both variables can be established because other determinants like infections, temperature, weather change influences, in door pollution etc., could not be excluded. Evaluation of NO levels over 3 years and dust levels over a test period of 1 year showed no statistical relationship with corresponding croup incidence.

Among a population of 18,175 children below 7 years of age in medium sized towns and rural areas in south-western Germany 552 (3.03%) cases of croup were registered during a 12 months period in 1984-85 by their physicians. Distributions according to months, sex and age at the onset of the disease were the same as in other recent investigations: The level of the air-pollution measured (SO2, NOx, CO, CO2, ozone and dust) was low (highest monthly means in microgram/m3: SO2 88, NO2 73, NO 119, dust 41). There was no relevant influence of the degree of air pollution on croup-frequency. The rise of croup-frequency shortly after a period of several days of higher pollution was accompanied by an influenza epidemic as proved by virus isolations.

A total of 1470 hospitalized children with croup in the cities of Bochum and Herne were examined over a period of 19 years, with the aim of checking whether there was any relationship between croup incidence and changes in different weather parameters such as temperature, air pressure, absolute and relative air humidity, and wind speed. The incidence of croup was seasonal, being higher in the months of January, February, and March and from September to December. Statistical evaluation by discriminant analysis, t-test and chi 2-test showed a significant correlation (alpha greater than or equal to 0.95) between croup incidence and individual weather parameters in some months. The results seem to indicate a higher frequency of croup after decreases in temperature and influx of dry air masses (decreases in absolute humidity). In some months an increased incidence of hospitalized children with croup was observed after decreases in air pressure and during weather with extremely high (w greater than 4.5) or low (w less than 1.5) wind speed. In summary, no clear and consistent relationship between incidence of croup and particular weather parameters could be found.