| Agent | Toxigenic C. diphtheriae (tox gene via β‑phage) | B. pertussis (pertussis toxin) | C. tetani spores (tetanospasmin) |
| Reservoir | Humans; carriers outnumber cases | Humans; adolescents and adults with waning immunity are key sources for infants | Soil, animal and human faeces |
| Transmission | Droplets, contact (cutaneous) | Droplets; SAR in households up to 90% in the unimmunised | Wounds, unclean cord care, unsafe abortion or injection; not communicable |
| Incubation | 2–5 days | 7–14 days (up to 21) | 3–21 days (usually about 8); neonatal 3–28 days (usually 7) |
| Communicability | Up to 2 weeks untreated; carriers longer | Catarrhal stage and first 3 weeks of paroxysms (most infectious early) | None |
| Clinical | Grey‑white adherent pseudomembrane, bleeds on removal; bull neck; myocarditis (2nd week), palatal/ocular palsy (3rd–6th week) | Catarrhal (1–2 weeks) → paroxysmal (whoop, post‑tussive vomiting, apnoea in infants) → convalescent | Trismus, risus sardonicus, opisthotonos, spasms with intact sensorium |
| Diagnosis | Throat swab culture (Loeffler's, tellurite media), Elek test for toxigenicity, PCR | Nasopharyngeal swab PCR/culture; lymphocytosis | Clinical |
| Treatment | Diphtheria antitoxin (DAT) urgently on clinical suspicion + penicillin/erythromycin; airway; cardiac monitoring | Azithromycin; supportive; infants admitted | TIG, wound care, metronidazole, spasm control, ICU |