Toxin-Mediated Infections: TSS, Botulism, Tetanus & Diphtheria

Principles of toxin-mediated disease

The toxin does the damage. A modest bacterial burden releases an exotoxin, so cultures may be negative, symptoms can outlast the infection, and the diagnosis is clinical. Treatment starts on suspicion: remove the source, neutralize circulating toxin (antitoxin, immune globulin, IVIG; none can recall toxin already bound), and stop further production (protein-synthesis inhibitors, bactericidal antibiotics, debridement).

Toxic shock syndrome

Superantigens. S. aureus TSST-1 (or enterotoxins B and C) and group A strep exotoxins SpeA and SpeC clamp MHC class II to the T-cell receptor Vβ region outside the peptide groove, activating up to 20% of T cells → IL-1, IL-2, TNF-α and IFN-γ → capillary leak, shock, and multiorgan failure.

Staphylococcal TSS. Menstrual cases follow retained or high-absorbency tampons; nonmenstrual cases follow nasal packing, postpartum or surgical wounds (often bland-looking), and burns. Criteria: fever ≥38.9 °C, SBP ≤90 mmHg, diffuse macular "sunburn" erythroderma, and ≥3 organ systems (vomiting or diarrhea, myalgia or CK >2× normal, conjunctival/oral/vaginal hyperemia, renal or liver tests ≥2× normal, platelets <100,000/μL, disorientation). Palms and soles desquamate 1–2 weeks later, confirming the diagnosis in retrospect.

Streptococcal TSS. Usually complicates necrotizing fasciitis or myositis, after varicella in children, blunt muscle injury, surgery, or childbirth. Pain out of proportion to skin findings precedes shock, rash is less common, and kidney injury, coagulopathy, and ARDS follow.

Eagle effect: penicillin works poorly against dense, slow-growing group A strep inocula because penicillin-binding proteins are down-regulated; clindamycin is unaffected by inoculum size and also suppresses toxin and M-protein production.

Botulism

Mechanism and sources. C. botulinum, an anaerobic gram-positive spore-former, makes a zinc protease that cleaves SNARE proteins (type A cleaves SNAP-25), blocking acetylcholine release at the neuromuscular junction and cholinergic autonomic synapses. Foodborne disease is intoxication with preformed toxin from home-canned low-acid foods (types A, B, E; E from fermented fish), sometimes preceded by vomiting 12–36 h after the meal. Wound botulism (subcutaneous black-tar heroin) and infant botulism arise from spores germinating inside the body.

Presentation. An afebrile, alert patient develops symmetric descending flaccid paralysis: cranial nerves first (diplopia, ptosis, dysarthria, dysphagia), then neck and arms, respiratory muscles, and finally trunk and legs. Dilated sluggish pupils, dry mouth, constipation, and urinary retention reflect autonomic blockade; sensation is normal. Guillain-Barré ascends with paresthesias and high CSF protein; myasthenia is fatigable and spares the pupils.

Treatment. Toxin assays take days, so call the health department or CDC for heptavalent equine antitoxin (BAT) on suspicion. It neutralizes circulating toxin and halts progression but cannot reverse paralysis; recovery needs new nerve terminals over weeks to months. Follow vital capacity and inspiratory force serially, intubate early, and for wound botulism debride and give penicillin G after antitoxin. A single case is a public-health emergency.

Avoid aminoglycosides in botulism: they deepen the neuromuscular blockade.

Infant botulism. Spores from honey or soil and construction dust colonize the immature gut of infants <1 year: constipation first, then poor suck, weak cry, ptosis, and hypotonia. Give BabyBIG (human-derived botulism immune globulin IV) and respiratory support; antibiotics are avoided. No honey before 12 months.

Tetanus

Mechanism. C. tetani spores from soil enter puncture wounds, burns, injection sites, or a newborn's umbilical stump (unvaccinated mother). Tetanospasmin travels retrograde up motor axons to the spinal cord and cleaves synaptobrevin in Renshaw inhibitory interneurons, blocking glycine and GABA release → unopposed motor firing. Strychnine, a glycine-receptor blocker, mimics the picture.

Presentation. Typically 3–21 days after injury: trismus (often first), risus sardonicus, neck and back rigidity with opisthotonos, dysphagia, and agonizing spasms triggered by noise or touch, with intact consciousness. Laryngospasm and autonomic storms (labile blood pressure, tachyarrhythmias, fever) are the main killers. Diagnosis is clinical; wound cultures are unreliable. Mimics include strychnine poisoning, drug-induced acute dystonia (reverses with benztropine or diphenhydramine), and hypocalcemic tetany.

Treatment. Human tetanus immune globulin IM (neutralizes unbound toxin only), metronidazole, and debridement; benzodiazepines for spasms, adding magnesium or neuromuscular blockade if refractory; a dark, quiet room; early airway control. Disease confers no immunity, so give a full tetanus toxoid series at a separate site.

Diphtheria

Organism and toxin. Only C. diphtheriae strains carrying the β-prophage tox gene are toxigenic; the toxin ADP-ribosylates elongation factor-2 (like Pseudomonas exotoxin A). It grows on tellurite or Loeffler medium, and the Elek test proves toxin production.

Presentation and treatment. An unvaccinated patient has sore throat, an adherent gray pseudomembrane that bleeds when scraped, and massive neck swelling (bull neck) that can obstruct the airway. Myocarditis with heart block usually appears in weeks 1–2, followed by cranial (palatal), then peripheral, neuropathy. Give equine antitoxin (via CDC) on suspicion, erythromycin or penicillin for 14 days, droplet isolation, and cardiac monitoring; culture, prophylax, and boost close contacts.