2451. Hospital-acquired Legionella Pneumonia Outbreak at an Academic Medical Center. A Case–control Study of Risk Factors

Background An outbreak of hospital-acquired Legionella pneumonia, associated with potable water contamination, occurred at our university hospital in November of 2018, despite a longstanding copper-silver ionization system. We conducted a case–control study to examine risk factors for Legionella pneumonia. Methods We matched controls to cases by dates of admission, hospital ward, and admitting service, in a 4:1 ratio. We reviewed patient charts for potential risk factors and exposures, and summarized demographic information using descriptive analyses. Univariate and multiple logistic regression analyses were also performed. We used pulsed-field gel electrophoresis for molecular typing of isolates from patient respiratory samples and hospital water samples. Results We identified 13 cases of nosocomial legionella pneumonia over a one-month period (Figure 1), with 8 males, 5 females, and a mean age of 63 years. The average time to diagnosis was 19 days following admission. Six patients were transplant recipients – two had solid organ, and six had bone marrow transplant. Urinary Legionella antigen was positive in all cases. Table 1 shows predictors for Legionella pneumonia in univariate analyses. Current smoking (OR = 7.5, 95% CI [1.11 – 50.84], p = 0.03], pre-admission steroid prescription (OR = 6.5, 95% CI [1.65 – 26.20], p = 0.008], documentation of shower (OR = 6.2, 95% CI [1.54 – 25.82], p = 0.01], and number of showers prior to hyper-chlorination (OR = 1.45, 95% CI [1.03 – 2.04], p = 0.03] were significant risk factors on univariate analysis. The multiple regression model was also significant (P < 0.001) with all of the above-identified predictors (Table 2). Molecular typing found Legionella strains from patient respiratory samples and water samples to be identical. Multiple interventions, including restriction of showering, hyper-chlorination, and optimization of water flow through the copper-silver ionization system were implemented, and were successful in mitigating the outbreak. Conclusion We found showering to be a modifiable risk factor for Legionella pneumonia in this outbreak. Interventions to reduce this risk might include point of use filters in showers in high-risk populations. Disclosures All authors: No reported disclosures.