US Salmonella outbreak linked to microbiology laboratories

Public health officials in several US states have identified an outbreak of Salmonella Typhimurium infections linked to various clinical, commercial, and college and university teaching microbiology laboratories.

Public health investigators used PulseNet — the national subtyping network of public health and food regulatory agency laboratories — to identify illnesses that may be part of the outbreak. Coordinated by the Centers for Disease Control and Prevention (CDC), PulseNet performs DNA fingerprinting on Salmonella bacteria isolated from ill people by using pulsed-field gel electrophoresis (PFGE) and whole genome sequencing (WGS). PulseNet manages a national database of these DNA fingerprints to identify possible outbreaks.

Twenty-four people infected with the outbreak strain of Salmonella Typhimurium have been reported from 16 states, including California, Colorado, Florida, Georgia, Iowa, Maine, Michigan, Missouri, North Carolina, New Hampshire, New Jersey, New Mexico, New York, Oklahoma, Texas and Washington. WGS showed that the strain of Salmonella Typhimurium causing illness in this outbreak is closely related genetically to a strain from outbreaks in 2014 and 2011, both of which were linked to microbiology laboratories. As a result of the 2011 outbreak, several laboratory professionals across the country developed a set of guidelines for handling microorganisms safely in a teaching laboratory.

In interviews that took place during the current outbreak, ill people answered questions about different exposures in the week before they became ill. Nine (69%) of 13 ill people had laboratory exposures. Ill people also reported behaviours while working in the laboratory that could increase the risk of Salmonella infection. These included not wearing gloves or lab coats, not washing hands, and using the same writing utensils and notebooks outside of the laboratory.

The outbreak thus highlights the potential risk of Salmonella infection associated with working in microbiology laboratories, emphasising the need for all students and staff in clinical and teaching microbiology laboratories to receive laboratory safety training. Either nonpathogenic or attenuated bacterial strains should be used when possible, especially in teaching laboratories. This practice will help reduce the risk of students and their family members becoming ill.