Higher number of hospital admissions for bronchiolitis with lower mean ambient temperature

Abstract

Background During our work as general practitioners (GPs) in Malta and during attachments in the Paediatric Department of the main hospital in Malta, we encountered children with bronchiolitis. Bronchiolitis has been described as a seasonal viral illness characterised by breathing difficulties, cough, poor feeding, irritability and lethargy and, in the very young, apnoea (SIGN, 2006). We speculated that there were more bronchiolitis-related admissions to hospital during colder temperatures, but could not find any literature on the local patterns of this illness. International literature described a specific seasonality of bronchiolitis in the northern hemisphere, with more admissions being recorded in the winter months (Centers for Disease Control and Prevention (CDC), 2010; Chen et al., 2014; Coffin, 2005; Grimprel, 2001; Grimwood et al., 2008; Hervás et al., 2012), specifically with colder temperatures (Chen et al., 2014). In a concurrent study, we established seasonality and recorded other epidemiological features of the condition (Casha et al., 2015). Objectives The aim of this retrospective study was to identify the temperature range in which most hospitalizations for bronchiolitis occur, and to determine if there is a significant difference between the number of admissions and the set mean ambient temperature categories (arbitrarily set as below 10°C, between 10.1 and 15°C, between 15.1 and 20°C, between 20.1 and 25°C and between 25.1 and 30°C). The null hypothesis is that there is no significant difference in number of hospital admissions between each mean ambient temperature group and the alternative hypothesis is that there is a difference. This was done with a view to providing a better understanding of the condition to guide both clinical and policy decisions. Method The four-year period January 2008 to December 2011 was chosen. Statistical data was obtained from the Department of Health Information and Research to define the dates of admission for all recorded episodes of hospital admission for bronchiolitis among infants or children under two years at Mater Dei Hospital, the main Maltese hospital, for this period. Temperature records for the same period were obtained from the Maltese Meteorological Office. Appropriate statistical tools were used to assess the relation between admission rate and temperature. The diagnosis leading to the classification of the admission as one for bronchiolitis was validated by examining a significant sample of doctors’ notes in the relevant patient files and matching these against clinical criteria for diagnosis (SIGN, 2006). Results Our findings show that the majority of admissions occur between 10.91°C and 18.61°C. The nonparametric Kruskal-Wallis equality-of-populations rank test proved that there is a statistically different admission frequency between different mean ambient temperature categories. Conclusions In Malta, a higher number of hospital admissions for bronchiolitis among infants or children under two years occurs when mean ambient temperature is lower. This is in keeping with international literature.