Disinfecting power of multi-purpose soft contact lens disinfecting solutions on fungi colonising the conjunctiva and environmental air isolates

Abstract number: P1038

Ma C., Boost M.V., Cho P.

Objectives: There has been increasing concern about fungal corneal infections since the outbreak of Fusarium infections in 2005 in soft contact lens wearers, which led to withdrawal of one multi-purpose disinfecting solution (MPS). Although FDA guidelines require MPS to reduce numbers of a type strain of Fusarium solani by one log dilution, their effectiveness on other strains is not routinely tested. Poor compliance with lens care routines and rubbing of the eyes can introduce fungi into the eye. This study investigated effectiveness of soft contact lens MPS against commensal and environmental fungal isolates.

Methods: The lower conjunctival surface and eyelashes of 30 subjects aged 20–24 were swabbed with a saline-moistened swab and cultured on potato dextrose agar with chloramphenicol (PDAc). Environmental fungi were obtained from ten cultures of PDAc exposed for 30 minutes in urban areas near to flower beds and lawns. Plates were incubated at 25^°C for 7 days and fungal isolates sub-cultured, identified, and used as challenge strains against three soft lens MPS solutions using the stand-alone test required by FDA Guidelines. F. solani (ATCC 36031) was used as a control.

Results: Sixteen subjects were colonised with fungal organisms yielding a total of 23 isolates. Air sampling yielded a further 14 isolates. Isolates were mainly Penicillium (38%) and Aspergillus (30%) species, the latter being an ocular pathogen. Both MPS "A" and "B", which contain polyhexamethylene biguanide (PHMB), failed to achieve a one log reduction for any of the isolates though the reduction of F. solani was 1.3 log. MPS "C" which contains POLYQUAD was able to achieve a 1.0 or greater log reduction for all isolates.

Conclusions: MPS containing PHMB failed to successfully reduce viable fungal numbers by one log, although able to meet FDA Guidelines for the test strain of F. solani. Failure to inhibit such strains may increase the risk of ocular infection in contact lens wearers, as infections may be caused by other fungal pathogens, particularly Aspergillus spp. and poor compliance with lens care routines may lead to contamination with fungi. In the light of recent increase in microbial keratitis of fungal aetiology, changes to FDA guidelines to expand numbers of strains and species may be appropriate.