Diagnosis - Microbial Food Poisoning

Diagnosis

Food-borne botulism

·              Laboratory analysis: Samples of serum, stool, vomitus, gastric contents, and suspected food item should be tested for Cl. botulinum as well as botulinum toxin. The specimens should be handled cautiously, refriger-ated, and examined as soon as possible after collection. Stool specimens must be incubated anaerobically and subcultured on egg yolk agar.

The usual procedure is to draw 10 ml of serum before treatment has begun, for determination of toxin. The standard laboratory study is the mouse bioassay. Analysis takes 24 hours to perform, so the results cannot be used to determine treatment. Mouse bioassay for botulinum toxins is extremely sensitive and detects as little as 5 to 10 pg toxin/ml. ELISA tests have not been shown to have the same sensitivity as the mouse bioassay.

Diagnosis is confirmed by demonstration of toxin in serum, stool, or food items, or by isolation of organism in stool or food items.

·              Tensilon test: Tensilon (edrophonium) is a rapid-acting anticholinesterase used to differentiate botulism from myasthenia gravis. 10 mg of the drug is injected IV slowly (1 to 2 mg at first, followed by the remainder over the next 5 minutes). Muscle strength in myasthenia gravis will improve dramatically within ½ to 1 minute, and last for about 5 minutes, while there will be little or no improvement in botulism.

·              Electromyography: In all forms of botulism, the EMG pattern is characterised by brief, small, abundant motor unit action potentials. Motor nerve conduction velocity is normal. Another characteristic EMG finding is an increment of small compound muscle action potential amplitude directly related to the release of acetylcholine following repetitive stimulation at 20–50 Hz.

·              Bedside spirometry to determine forced vital capacity (FVC) and inspiratory force should be done sequentially in suspected patients. These tests may provide early clues of impending respiratory failure. Arterial blood gases may show only minor abnormalities despite substantial loss of ventilatory reserve.

·              Experimental and clinical evidence suggests that botulinum toxin may exert a direct cardiac effect.

Intraventricular conduction delay, non-specific ST-T wave changes, and arrhythmias, including sudden death from ventricular fibrillation, have all been reported.

Wound botulism

·      Laboratory analysis: Wound cultures and serum assays for botulinum toxin.

·      Tensilon test.

·      Electromyography.

Infant botulism

·      History: of honey ingestion.

·      Clinical picture.

·      Tensilon test: unreliable in infants.

·      Stool analysis.