A mysterious cluster of deadly bloodstream infections in Wisconsin has set state and federal disease detectives scrambling to understand why a common and generally harmless microbe is suddenly wreaking such havoc.

The outbreak has killed 15 people and sickened 33 others in a cluster of counties surrounding Milwaukee.

Public health authorities know what’s causing the illnesses: a species of bacteria named Elizabethkingia anophelis....

...State and federal investigators are testing tap water, skin care products, and other products patients may have ingested or come in contact with as a possible source of contamination. The vast majority of specimens share a matching genetic fingerprint, indicating a common source for the outbreak.

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