Purpose. To determine the rate and type of microbial contamination when contact lens cases are air-dried in two different positions (face up and face down) and in four different locations (toilet, bathroom, office, and bedroom).
Methods. Unused contact lens cases (n = 97) were rinsed with 2-ml sterile phosphate buffered saline and then placed on facial tissue paper in different locations: humid (toilet and bathroom) and non-humid (office and bedroom) and air-dried at room temperature. After 24 h, the contact lens cases were collected and sampled for microbial numbers and microbial types identified using standard techniques. The microbial profile and the rate of contamination between different locations and positions were compared.
Results. Irrespective of the air-drying location, contact lens cases positioned face up had a significantly higher contamination rate (34/48, 71%) compared with contact lens cases air-dried face down (6/49, 12%) (p < 0.001). For those contact lens cases air-dried face up, there was more contamination when placed in humid environments (toilet and bathroom) than in the non-humid environments (office and bedroom) (p = 0.01). However, the contact lens case contamination rate among various locations was similar when contact lens cases were air-dried face down. Total microorganisms recovered from contact lens cases ranged from 0 to 275 colony forming unit per well. The most frequently recovered microorganisms from the contaminated contact lens cases were coagulase-negative Staphylococci, fungi, and Bacillus spp. Thirty-three percent (13/40) of contact lens cases were contaminated with multiple species.
Conclusions. Small numbers of microorganisms from the environment may contaminate contact lens cases while cases are air-dried face up. Cases air-dried in humid environments have higher levels of microbial contamination; this is particularly true when contact lens cases are positioned face up. On the basis of this limited study, we would recommend contact lens cases be air-dried face down.