Climatic influence on conjunctival bacteria of patients undergoing cataract surgery

To describe the monthly prevalence of conjunctival bacteria in patients undergoing cataract extraction and the possible climatic influence on it, in Madrid, in order to clarify postsurgical endophthalmitis pathogenesis.

The lower conjunctival content sample of 4432 consecutive patients awaiting cataract surgery was cultured from January 1994 to December 1996. The dates of the operations and the rehospitalization for postsurgical endophthalmitis, if this took place, were checked. The isolated bacteria were grouped to study the statistical significance of the differences in the monthly prevalence differences (chi2 tests). Temperature and relative humidity are given monthly for the area where our patients live.

The total frequency of the conjunctival bacteria increases in April, May, and June, when the daily average temperature rises from 12 to 22 degrees C and the relative humidity oscillates between 45 and 60% in our area. Bacteria groups' frequency was significantly higher as follows: Staphylococci coagulase negative ( > 60%) in April, May, and June; Corynebacterium sp ( > 33%), Staphylococcus Aureus ( > 8%), and other Gram-positive bacteria ( > 2.5%) in May; Streptococcus Pneumoniae increases ( > 3.4%) in March, November, and December; Haemophilus sp ( > 3.4%) in January and April; Gram-negative Cocci ( > 3%) in April; and other Streptococcus sp ( > 6%) in April, May, and September. Our incidence of rehospitalization for endophthalmitis after cataract extraction in May and June together was 3.37 times higher than in the other months.

Conjunctival bacteria of our patients undergoing cataract surgery present a seasonal prevalence pattern, which could be considered as a predisposing condition for having postsurgical endophthalmitis in certain months.