On-site Gram staining that increases a post-test probability of an ominous infection: a case of necrotizing fasciitis caused by Vibrio vulnificus: a case report

Abstract Background Gram staining is a classic but standard and essential procedure for the prompt selection of appropriate antibiotics in an emergency setting. Even in the era of sophisticated medicine with technically developed machinery, it is not uncommon that a classic procedure such as Gram staining is the most efficient for assisting physicians in making therapeutic decisions in a timely fashion. Case presentation A 65-year-old Asian man with alcoholic cirrhosis complicated by esophageal varices was brought to the emergency division of Saga Medical School Hospital in early August, complaining of severe pain, redness, swelling, and purpura of the lower extremities. On physical examination he appeared in a critically ill condition suggestive of deep-seated soft tissue infection, raising a pre-test probability of streptococci, staphylococci, Vibrio sp., or Aeromonas sp. as a causative pathogen. A characteristic of his residency in an estuarine area is that raw seafood ingestion, as documented in this patient prior to the current admission, predisposes those who have a chronic liver disease to a life-threatening Vibrio vulnificus infection. Given the pathognomonic clinical features suggestive of necrotizing fasciitis, our immediate attempt was to narrow down the differential list of candidate pathogens by obtaining clinical specimens for microbiological investigation, thus inquiring about the post-test probability of the causative pathogen. The Gram stain of the small amount of discharge from the test incision of the affected lesion detected Gram-negative rods morphologically compatible with V. vulnificus. After two sets of blood culture, intravenous meropenem and minocycline were immediately administered before the patient underwent emergency surgical debridement. The next day, both blood culture and wound culture retrieved Gram-negative rods, which were subsequently identified as V. vulnificus by mass spectrometry, matrix-assisted laser desorption/ionization. The antibiotics were switched to intravenous ceftriaxone and minocycline. Conclusion The pre-test probability of V. vulnificus infection was further validated by on-site Gram staining in the emergency division. This case report highlights the significance of a classic procedure