Overview of the microbiological contamination of eye dropper inserts and caps: influence on the content sterility and the risk of ocular infection

Context
The manufacturing process for eye drop batches ensures the content sterility from production to opening. One of the challenges is to maintain sterility during patient use. Our production unit has evaluated the microbiological contamination of dropper inserts and the inner surface of eye dropper bottle caps along with its impact on the sterility content and the risk of eye contamination.

Methods
Eye drop bottles produced by the unit were collected from the ophthalmology ward and the outpatient department of the hospital. The dropper inserts and the inner surface of the caps were sampled using flocked swabs (eSwab^®) and cultured on Columbia agar containing 5% horse blood, incubated for 3 days at 37°C. The sampling method was validated beforehand. Microorganisms were identified by MALDI-TOF-MS (matrix-assisted laser desorption/ionization time-of-flight, mass spectrometry). If the insert and/or cap were contaminated, the vial residual content were cultured using routine sterility testing techniques employed by the control laboratory (membrane filtration sterility testing and BACT/ALERT^® technique).

Results
From January 17^th to May 17^th (4 months), 157 vials were collected. Among the 110 usable bottles, 72 (65%) came from hospitalization and 38 (35%) from outpatient department. The main eye drops collected from hospital inpatients were antibiotics (90%), while the majority of those collected from outpatients were immunosuppressants (84%). Thirty-six bottles were contaminated, included 3 (8%) from ophthalmology department and 33 (92%) from outpatients. The main germs identified were commensal and environmental germs, including potential pathogens. One yeast was also isolated (Candida parapsilosis). The majority of bottles (67%) were contaminated simultaneously at both sites (insert and inside of cap). Of the 36 bottles contaminated, the contents of one were also contaminated with the same germ.

Discussion-conclusion
The results obtained highlight several factors involved in the contamination of eye-drops bottles, which is line with the literature (1) : the setting of use, the type of contaminated eye-drops, the microorganisms isolated, the contaminated part of the bottle and microbial migration between these sites. One prospect is the integration of antimicrobial technology into the vial material to prevent contamination.

1. Iskandar K, Marchin L, Kodjikian L, Rocher M, Roques C. Highlighting the Microbial Contamination of the Dropper Tip and Cap of In-Use Eye Drops, the Associated Contributory Factors, and the Risk of Infection: A Past-30-Years Literature Review.