Profile and frequency of microbial contamination of contact lens cases.

PURPOSE

To evaluate the frequency level and profile of contact lens storage case contamination in asymptomatic contact lens wearers and to examine whether different areas of the same lens case may show a different rate and profile of contamination. The relationship between lens storage case contamination and the age of the lens storage case was also examined.

METHODS

Sixty-four lens cases and case age information were collected from asymptomatic contact lens wearers. Lens cases were sampled at two locations, the upper rim and the lower base. The samples underwent microbiological investigation for recovery of bacteria and fungi. Contamination rate between the two sampling locations and the relationship between the contamination levels and the age of the lens case were analyzed.

RESULTS

Contamination occurred in 58% (37 of 64) of lens cases. The most frequently recovered microorganisms were coagulase-negative Staphylococci (51%, 19 of 37), Bacillus spp. (43%,16 of 37), and fungi (27%,10 of 37). For flat-well lens cases, higher numbers of microorganisms were recovered from the upper rim than that from the lower base (p = 0.02), and a greater variety of Gram-negative bacteria were recovered from the upper rim. A higher recovery rate of Micrococcus spp. (p = 0.02; in flat cases) and coagulase-negative Staphylococci (p = 0.01; for both flat and basket type cases) was found from the base of the case well compared with the upper rim. For stand-up cases, higher numbers of microorganisms were recovered from the lens basket compared to the upper hinge (p = 0.047). Lens cases that were <9 months of age had lower levels of contamination (p = 0.013) than older cases.

CONCLUSIONS

Frequent replacement of lens cases may reduce microbial contamination. Future studies should specify the areas swabbed in the lens case. Better lens storage case design and additional hygiene attention need to be introduced to reduce contamination in these "risky" areas.