Bacterial colonization of the oropharynx is the initial event in most lower respiratory tract infections. To study the role of bacterial adherence in lower respiratory tract infections caused by Branhamella catarrhalis (B. catarrhalis) in winter, in vitro adherence assays of the organism to human oropharyngeal cells were carried out in winter, spring, summer and autumn. A total of 57 adults of both sexes were studied from January to December 1985. Forty eight persons of 57 had chronic pulmonary diseases and the remaining 9 persons had other clinical entities and served as the control group. Predominance of lower respiratory tract infections caused by B. catarrhalis with high adherence rate was observed in winter. Adherence activity was moderate in spring and autumn and low in summer and accompanied by a similar incidence of lower respiratory tract infections with this bacteria. In addition, similar results were found in patients in whom investigations were done successively in the above four seasons. Bacterial adherence activity to cells however, was weak in winter in the control group. These results indicate that seasonal variation plays a significant role in the ability of B. catarrhalis to adhere to oropharyngeal cells. This is an important pathogenic factor correlated with the incidence of lower.respiratory tract infections in these patients. Branhamella catarrhalis ; adherence ; lower respiratory tract infections ; seasons

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