Cluster of postinjection abscesses related to corticosteroid injections and use of benzalkonium chloride

Benzalkonium chloride (BC) is an unreliable disinfectant. A matched case-co ntrol study and environmental investigation were conducted to determine the cause of and risk factors for a cluster of postinjection abscesses at a pr ivate medical clinic where BC was used as a disinfectant. Twenty-eight case -patients who had an abscess at the injection site were matched with 126 co ntrol patients who had received an intramuscular injection at the clinic on the same day. Risk factors for abscess development in a multivariable logi stic model were corticosteroid injection and being female. All case-patient s had received a corticosteroid injection from a multidose vial. Cultures o f abscesses from 20 of 23 case-patients grew Pseudomonas aeruginosa. Cultur es of BC prepared at the clinic also grew P aeruginosa, suggesting that BC was the source of infection. Injection site cleaning with BC did not appear to be the route of infection since use of BC at the time of injection was not associated with abscess development. A more likely route of infection w as injection of contaminated corticosteroid from multidose vials that could have been inoculated with pseudomonads via needle puncture after vial sept a were wiped with contaminated BC. Benzalkonium chloride should not be used to clean injection vial septa or injection sites.