Question
Read the following clinical history and answer the following questions: A young adult male met with an accident on the high way and sustained severe injury to the right thigh. On examination there was foul smelling discharge and crepitus at some of the areas.
- (a) What is the probable diagnosis 1 mark(s)
- (b) Name the etiological agents 2 mark(s)
- (c) What are the specimens to be sent for the laboratory 2 mark(s)
- (d) Describe the laboratory diagnosis briefly 4 mark(s)
- (e) What is the prophylaxis. 1 mark(s)
Answer
a) Probable diagnosis: Gas gangrene (clostridial myonecrosis) — a deep, contaminated traumatic wound with foul-smelling discharge and crepitus (gas in the tissue) is the classical presentation.
b) Etiological agents: Clostridium perfringens (most common cause, ~80% of cases), also Clostridium septicum, Clostridium novyi, and Clostridium histolyticum — anaerobic, spore-forming, Gram-positive bacilli that contaminate deep wounds with devitalized tissue.
c) Specimens for laboratory
- Wound exudate/discharge collected anaerobically (in an anaerobic transport medium, avoiding air exposure).
- Necrotic muscle/tissue biopsy from the affected area (higher yield than surface swab).
- Blood culture, since bacteraemia/toxaemia can occur in severe/disseminated disease.
- Gas/fluid aspirate from crepitant tissue if present.
d) Laboratory diagnosis
- Direct Gram stain of the exudate — shows large, Gram-positive (often decolorizing to Gram-variable in older cultures), box-car shaped bacilli, characteristically with absent or few spores in the wound sample and, importantly, a paucity of inflammatory (pus) cells relative to the number of organisms — a distinguishing microscopic clue.
- Anaerobic culture on blood agar incubated anaerobically — C. perfringens shows rapid growth with a characteristic “double zone of haemolysis” (inner zone of complete haemolysis from theta toxin, outer zone of partial haemolysis from alpha toxin); “stormy clot” reaction in litmus milk medium.
- Nagler’s reaction — demonstrates lecithinase (alpha toxin) activity on egg-yolk agar, inhibited by specific antitoxin on one half of the plate — confirms toxin production.
- Radiology — soft-tissue gas seen on plain X-ray/CT supports the clinical diagnosis.
e) Prophylaxis Early, thorough surgical debridement of all devitalized/necrotic tissue and foreign material (removes the anaerobic environment required for spore germination); prophylactic antibiotics (penicillin) for contaminated wounds; hyperbaric oxygen therapy as an adjunct in established cases; prompt wound care after trauma to prevent anaerobic conditions from developing.