Notes from the Field: Salmonella from phlebotomy!
The Centers for Disease Control and Prevention have reported an outbreak of Salmonella infection in January 2013. Two of the patients almost certainly contracted their infections via frozen mice used to feed reptiles, a topic which we have warned readers about before. The individual in the third case had not come into contact with any feeder mice and didn’t have any pet reptiles, but was a phlebotomist at the hospital where the first two patients had been treated. Hospital records indicated that the phlebotomist had drawn blood from the first two patients on January 14th, three days before the onset of their own symptoms. According to the hospital infection control specialist, the phlebotomist reported the use of gloves while performing the procedure. Ultimately, all cases in this outbreak resolved with treatment.
I wanted to follow up on two things from the CDC report; one clinical and one biological. From a clinical standpoint, this case should not have happened. Although Salmonella infection is common overall, there are very few reports in the medical literature about health care workers acquiring this disease from an occupational exposure. The CDC indicates that this case is notable as it is the very first one where a health care worker has acquired a Salmonella infection during the act of drawing blood. Health care workers must remain vigilant about the risks associated with any infectious agents that their patients may be carrying, and regardless of those risks proper use of personal protective measures and infection control in the workplace must be followed in any case.
I was also struck by some of the nomenclature regarding the Salmonella isolates reported here. The Minnesota Department of Health performed a technique called Pulsed Field Gel Electrophoresis (PFGE), which distinguishes microbial isolates from one another based on differences in their genetic sequence. Salmonella strains are typically distinguished serologically, and a large number of distinct serovars exist that have differing abilities to cause disease. The isolate in this outbreak was described as Salmonella I 4,2:i:1,2. The designation is based on surface lipopolysaccharide antigens from the bacterial outer membrane, and flagellar antigens. The great advantage of serological testing is that results can be obtained very rapidly, however if a given serological test comes back negative, the clinician still does not know what the patient might have. Because of the complexity and diversity of the antigens found on Salmonella isolates, most local clinical laboratories will only carry a limited set of serological reagents for carrying out this type of isolate testing, which will enable them to confirm the present of the most significant disease causing strains.