Yes, piranha bite response is a pretty niche topic. Nevertheless, it’s interesting (at least to me).
A paper in Pediatric Emergency Care (An unexpected fish bite. Berkowitz and Goldsmith 2017) covers this topic. It starts off this way:
A 22-month-old boy presented to the pediatric emergency department with a missing right fourth distal phalanx. The story, according to his grandparents who were his guardians, was that they had been “fish sitting” for another one of their children and the child had put his hand into the fish tank. The fish, which, as it turned out, was a piranha, bit completely through the distal phalanx of the right fourth finger. The child’s grandfather reached into the tank, pulled out the piranha, gutted it, retrieved the intact piece of finger, and, along with the child, brought it on ice to an outside emergency department.
The question the authors decided to investigate was “Which antibiotics are appropriate?” since recommendations for animal bites are designed around bites from mammals, not fish. My initial thoughts would be that you need to cover against bacteria that as water associated (e.g. Pseudomonas, Aeromonas, Mycobacterium marinum), as well a those that live on human skin (since your own skin microbiota is a great source of infection). Not surprisingly, there’s not a lot of information in the literature about the best ways to protect from infections after a fish bite (or whether antibiotics are even indicated). The authors came up with similar concerns, and that led to a discussion of the best drug, considering the desire for an oral option, effectiveness of common oral drugs against some of these bacteria and potential issues using some drugs in young kids.
Their overall conclusions:
- Standard bite-response antibiotics are not great options because they don’t do a good job against some of the water-borne concerns (mainly Gram negative bacteria). They’re more focused on skin bacteria (mainly Gram positive bacteria).
- Despite concerns about not using fluoroquinolones when not clearly necessary, they figured ciprofloxacin best fit the bill as an oral option that covers the main concerns.
- The question of whether antibiotics are needed remains a case-by-case assessment, depending in large part on the bite location and severity.
Keeping fingers away from piranhas wouldn’t hurt either.