Outbreaks in hospital settings linked to faucet aerators and humidifiers are most commonly caused by which microorganism?

• A. Serratia marcescens
• B. Pseudomonas aeruginosa
• C. Klebsiella pneumoniae
• D. Salmonella spp.

Answer: (B)

Outbreaks tied to faucet aerators and humidifiers occur when a organism that loves moist environments takes hold in hospital water systems. Pseudomonas aeruginosa fits this scenario best because it thrives in damp niches, forms robust biofilms in plumbing, and can be easily dispersed as aerosols from humidifiers or faucet outlets. This opportunistic Gram-negative rod is notoriously able to persist despite routine cleaning, making it a common cause of water-source hospital infections, especially in vulnerable patients such as those who are intubated or have weakened immune systems. Infections can range from pneumonia to bacteremia and other device-associated infections, all linked to the moisture-rich habitats these devices create.

Serratia marcescens can be found in moist environments and can cause hospital outbreaks, but it is not as characteristically associated with faucet aerators and humidifiers as Pseudomonas. Klebsiella pneumoniae and Salmonella spp. are important nosocomial pathogens in different contexts (e.g., contaminated instruments, fluids, or foods for Salmonella), but their outbreaks are not as specifically tied to moist water systems or aerosolization from these devices.