Cluster of Postinjection Abscesses Related to Corticosteroid Injections and Use of Benzalkonium Chloride. Methods
Benzalkonium chloride (ВС) is an unreliable disinfectant. A matched case-control study and environmental investigation were conducted to determine the cause of and risk factors for a cluster of postinjection abscesses at a private medical clinic where ВС was used as a disinfectant. Twenty-eight case-patients who had an abscess at the injection site were matched with 126 control patients who had received an intramuscular injection at the clinic on the same day. Risk factors for abscess development in a multivariable logistic model were corticosteroid injection and being female. All case-patients had received a corticosteroid injection from a multidose vial. Cultures of abscesses from 20 of 23 case-patients grew Pseudomonas aeruginosa. Cultures of ВС prepared at the clinic also grew Paeruginosa, suggesting that ВС was the source of infection. Injection site cleaning with ВС did not appear to be the route of infection since use of ВС at the time of injection was not associated with abscess development. A more likely route of infection was injection of contaminated corticosteroid from multidose vials that could have been inoculated with pseudomonads via needle puncture after vial septa were wiped with contaminated ВС. Benzalkonium chloride should not be used to clean injection vial septa or injection sites.
Benzalkonium chloride is an unreliable disinfectant: Gram-negative organisms (eg, pseudomonads) often are resistant to benzalkonium chloride, and benzalkonium chloride’s efficacy is diminished when substances that adsorb the compound (eg, cotton balls or gauze) are immersed in it. The use of benzalkonium chloride in hospitals has been discouraged by the Centers for Disease Control and Prevention since 1976.
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In spring 1995, several patients at a private medical clinic in New Mexico began complaining of pain and swelling at the injection site after receiving intramuscular (IM) corticosteroid injections. Pseudomonas aeruginosa was later cultured from several patients’ abscesses, and the clinic discontinued these corticosteroid injections. The clinic had been using cotton balls soaked in alcohol or benzalkonium chloride to clean injection sites and injection-vial septa. The Office of Epidemiology of the New Mexico Department of Health (NMDOH) initi ated an investigation to determine whether use of benzalkonium chloride was the cause of this cluster of postinjection abscesses and to identify other risk factors for abscess development among clinic patients.
Methods
Epidemiologic Investigation
We defined a case as a patient with an abscess at the injection site that drained pus spontaneously or surgically following an injection at the clinic during January-June 1995. Case-patients were identified through the clinic, local surgeons, and patients’ attorneys.
We conducted a matched case-control study to identify risk factors for postinjection abscess development in patients receiving IM injections at the clinic. Through interviews with case-patients and review of their medical charts, we identified the day on which each of the case-patients received the injection associated with their abscess. All other patients receiving IM injections on those days served as controls. We reviewed medical records and interviewed case- and control-patients using a standard questionnaire. The questionnaire requested information regarding demographic factors, clinical signs and symptoms, and potential risk factors.
The following potential risk factors for abscess formation were assessed: age; sex; body mass index [BMI = weight in kg/(height in m)^2] in adults; presence of selected health conditions that affect the immune response—regular use of steroids, diabetes, chemotherapy or radiation therapy for cancer at the time of the injection, or other immunosuppressive conditions; injection site (gluteal versus deltoid); type of medication received (corticosteroid versus other); type of vial (multidose versus single-dose); individual administering injection; and type of disinfectant used to clean the injection site and injection-vial septum (benzalkonium chloride versus alcohol). The disinfectant used at the time of injection was assumed to be whichever disinfectant the person administering the injection had normally used during the months when case-patients received injections. All intramuscular injections were given by five clinic employees who were very consistent in their use of either benzalkonium chloride or alcohol as a disinfectant during that time period: Four reported using the same disinfectant 100% of the time, and one reported using the same disinfectant 80% of the time.
We calculated odds ratios (ORs) for each risk factor with respect to abscess development in accordance with a frequency matched design in which cases were matched with controls by injection date. Because of small cell sizes for some injection dates, we calculated conditional maximum likelihood estimates of the ORs using an exact estimation approach. We also assessed the independent contribution of risk factors when considered simultaneously in a conditional logistic regression model. The statistical software packages StatXact 3 for Windows and LogXact were used for the statistical analyses. Statistical significance was defined as a P value < .05. zelnorm canadian pharmacy
The investigation was conducted under the authority of the New Mexico Public Health Act; therefore, approval from an institutional review board was not sought. Consent was obtained from each patient before proceeding with the telephone interview.
Environmental and Laboratory Investigation
We asked clinic staff to prepare a stock solution of benzalkonium chloride in the same manner as was done before its use was discontinued prior to our investigation. Cultures were taken of cotton balls soaked in this solution. Other environmental samples from the clinic were benzalkonium chloride concentrate (17% Zephiran® Chloride), tap water, cotton balls soaked in alcohol, hand washes used by clinic personnel, swabs from the tops of eight opened multidose vials, and samples from the contents of two of these vials. All cultures were performed by NMDOH’s Scientific Laboratory Division (SLD) using standard methods.
The clinic returned unopened vials of triamcinolone acetonide (ТА), the most common corticosteroid used at the clinic, to the manufacturer (Steris Laboratories, Inc, Phoenix, AZ) for sterility testing. An opened vial of ТА and 18 opened multidose vials of other injectable medications (eg, estrogen, testosterone, vitamin B12, vaccines) from the clinic were sent to the US Food and Drug Administration (FDA) laboratory in Denver, Colorado for sterility testing.
Laboratory records were obtained for all case-patients whose abscesses were cultured. All available patient isolates were sent to SLD for identification confirmation using standard methods and for further categorization using the Microbial Identification System (MIS), which categorizes isolates based on fatty acid methyl esters of the cell wall. Patient isolates were also sent to the University of New Mexico Health Science Center, Molecular Epidemiology Laboratory for DNA fingerprint analysis using pulse-field gel electrophoresis.