Infectious Diseases — 5-min cram sheet
_Built from the infections disease index. Deck-faithful._
Buzzword → answer (the vignette reflex)
- Nikolsky sign +, flaccid blisters that shear, cleavage at stratum corneum, child <5 y → Staphylococcal scalded skin syndrome (SSSS; Rx flucloxacillin)
- TSST-1 superantigen, desquamation of palms + soles, tampon → Toxic shock syndrome (S. aureus)
- Strawberry tongue → raspberry tongue, circumoral pallor, blanching rash → Scarlet fever (erythrogenic toxin)
- Rich focus rupturing into basal cisterns, thick basal exudate, cranial-nerve palsies → Tuberculous meningitis
- India ink encapsulated yeast, "soap bubble" lesions, raised opening pressure → Cryptococcal meningitis (HIV CD4 <100)
- "Owl's eye" intranuclear inclusions, "pizza-pie" retinitis → CMV
- Heterophile antibody (Monospot) +, atypical lymphocytes, splenomegaly → EBV infectious mononucleosis
- Silver (Gomori methenamine) stain cup/boat-shaped cysts, diffuse ground-glass → Pneumocystis jirovecii pneumonia (PCP)
- Multiple ring-enhancing lesions in AIDS + serum anti-Toxo IgG → Cerebral toxoplasmosis
- Foamy histiocytes packed with acid-fast bacilli, CD4 <50 → Mycobacterium avium complex (MAC)
- "Blue beads" at apex of enterocytes, modified acid-fast oocysts in stool → Cryptosporidium parvum
- Halo sign + crescent sign, galactomannan, prolonged neutropenia → Invasive pulmonary aspergillosis
- Faget sign (relative bradycardia) + rose spots on abdomen, return from India → Enteric fever (typhoid)
- Eschar / tache noire at bite site, African game park → Tick typhus (Rickettsia)
- Councilman bodies in liver + Faget's sign + coffee-ground vomit → Yellow fever
- "Break-bone fever", saddleback (biphasic) fever, retro-orbital pain → Dengue
- Katayama fever + terminal haematuria, freshwater Africa → Schistosoma haematobium
- Cytoadherence "knobs" → sequestration, worst prognosis → P. falciparum
- Hydrophobia + tingling at bite site, dog bite → Rabies
- Risus sardonicus, trismus (lockjaw), tetanospasmin → Tetanus
- Descending flaccid paralysis, SNARE-protein cleavage (honey/canning) → Botulism
Bug → disease → drug
| Organism / condition | Disease / presentation | First-line drug (as index gives it) |
| S. aureus (MSSA) | skin / bloodstream / bone | Flucloxacillin (nafcillin / cefazolin) |
| MRSA | severe / complex infection | Vancomycin |
| MRSA pneumonia | (daptomycin inactivated by surfactant) | Linezolid |
| S. pyogenes (Group A Strep) | pharyngitis | Penicillin V 10 days |
| Scarlet fever | erythrogenic-toxin strep | Penicillin (drug of choice) |
| S. pneumoniae | pneumonia / asplenic bacteraemia | Ceftriaxone (immediate/empiric) |
| Enterococci | abdomino-pelvic sepsis / UTI / IE | Amoxicillin first-line (glycopeptide 2nd) |
| Listeria monocytogenes | meningitis (>55 y, pregnant) | Amoxicillin / ampicillin |
| C. diphtheriae | diphtheria | Antitoxin + erythromycin |
| Tetanus | wound + spastic paralysis | Human tetanus immunoglobulin + benzylpenicillin |
| Botulism | descending flaccid paralysis | Antitoxin + supportive (ventilation) |
| C. difficile | pseudomembranous colitis | Stop offending abx; oral metronidazole OR oral vancomycin |
| Nocardia | pneumonia + brain abscess | Co-trimoxazole |
| Actinomyces | mucosal (IUCD / dental) | Penicillin + local excision |
| Bacterial meningitis | empirical | IV ceftriaxone 2 g BD (+ amoxicillin if >60 y / immunocompromised) |
| Brain abscess | ring-enhancing lesion | 3rd-gen cephalosporin + metronidazole |
| HSV encephalitis | temporal-lobe | IV acyclovir 10 mg/kg tds 14–21 days |
| Cryptococcal meningitis | HIV | Amphotericin B + 5-flucytosine |
| Rabies | post-exposure | Human rabies Ig + human diploid cell vaccine |
| Herpes zoster (shingles) | dermatomal | Oral acyclovir 800 mg 5×/day ×7 d (within 72 h) |
| CMV | retinitis / colitis | IV ganciclovir (gold standard); intravitreal for retinitis |
| PCP (P. jirovecii) | HIV CD4 <200 | Co-trimoxazole (drug of choice) |
| Cerebral toxoplasmosis | multiple ring lesions | Sulphadiazine + pyrimethamine + folinic acid |
| Kaposi sarcoma | HHV-8 | ART (primary); intralesional vinblastine; IV doxorubicin |
| Anaphylaxis | shock + bronchospasm | Adrenaline SC 0.5 mg (first-line) + IV hydrocortisone |
| SJS / TEN | drug-induced | Stop drug + IVIg (first-line) |
| Febrile neutropenia | ANC <500 + fever | Immediate cefepime / meropenem / pip-tazobactam |
| Enteric fever | typhoid | Ceftriaxone 2 g IV OD then oral azithromycin 7 days |
| Tick typhus | eschar | Doxycycline 7 days |
| Amoebic liver abscess | RUQ pain, no diarrhoea | Metronidazole (or tinidazole) + diloxanide furoate |
| Malaria — non-falciparum | vivax / ovale | Chloroquine 600→300 mg + primaquine 15 mg ×14 d (check G6PD) |
| Malaria — falciparum | severe | IV quinine 10 mg/kg 8-hrly (+ doxy); or artemether-lumefantrine |
| Ebola | VHF | Supportive + ribavirin in the first week |
Criteria / staging / scores at a glance
- Fever definition — >37.2 °C before noon, >37.7 °C after noon.
- Classic FUO — >38.3 °C (101 °F) on several occasions, >3 weeks, no diagnosis despite 1 week inpatient OR 3 outpatient visits. Categories: Classic · Nosocomial · Neutropenic (neutrophils <500/µL) · HIV (>4 wk outpatient OR >3 days inpatient).
- CSF in meningitis — Bacterial: turbid, WBC ≥1000 PMN, protein ↑ (>1 g/L), glucose low, LDH raised. Viral: clear, <100 lymphocytes, glucose usually normal, LDH not raised. TB/fungal: lymphocytes, low glucose, high protein. Normal opening pressure <20 cm, WBC <5, protein <0.5 g/L, CSF:serum glucose <66%.
- Neutropenia — ANC <500/µL = serious-infection risk; <100/µL = severe. Febrile neutropenia = >38.3 °C single OR >38 °C sustained >1 h; high-risk = <100 for >7 days. ANC = WBC × (% neutrophils + % bands).
- HIV CD4 / OI risk — >500 none · 200–500 pneumococcus/TB/oral candida/Kaposi/VZV-HSV/molluscum · 100–200 PCP/PML(JCV)/histo/cocci · 50–100 toxo/crypto/cryptosporidium/CMV · <50 MAC + tissue-invasive CMV. CMV retinitis ~CD4 10; general OI once <50/µL.
- WHO severe malaria (P. falciparum) — cerebral malaria, severe anaemia, DIC, blackwater fever, hypoglycaemia, lactic acidosis, renal failure (ATN), algid malaria, pulmonary oedema/ARDS; + hyperpyrexia, hyperparasitaemia, jaundice, prostration.
- Dengue course — Febrile d1–3 · Critical d4–6 (platelet nadir, haematocrit peak) · Recovery d7–10 (fluid-overload risk). DHF/DSS needs ≥2 sequential infections with different serotypes; mortality up to 44%.
- EM / SJS / TEN spectrum — EM minor/major = typical targets (HSV, Mycoplasma), does NOT → TEN · SJS <10% BSA · overlap 10–30% · TEN >30% detachment; SJS/TEN = Type IV, drug-triggered (NSAIDs, antibiotics, antiepileptics).
- Immunodeficiency → pathogen — Humoral (myeloma/CLL/AIDS) → encapsulated (S. pneumoniae, H. influenzae) · T-cell (HIV/lymphoma/steroids) → intracellular + fungal · Neutropenia → Gram-negatives/Candida/Aspergillus · Complement → S. pneumoniae/Neisseria · Asplenia → encapsulated + Plasmodium.
- Herpesvirus family — Alpha: HSV-1, HSV-2, VZV · Beta: CMV, HHV6, HHV7 · Gamma: EBV (HHV4), KSHV (HHV8).
- Malaria species — falciparum variable (48 or 24 h, malignant tertian, recrudescence) · vivax/ovale 48 h tertian (relapse, hypnozoites → primaquine) · malariae 72 h quartan (longest) · knowlesi 24 h (shortest).
- Antimicrobial MOA — cell wall: β-lactams + glycopeptides · folate: trimethoprim/sulphonamides · DNA gyrase: quinolones · RNA polymerase: rifampicin · 50S: macrolides/chloramphenicol/lincosamides · 30S: tetracyclines/aminoglycosides.
- Stewardship (Start Smart Then Focus) — no antibiotics without evidence of bacterial infection; treat within 1 h for severe sepsis; review at 48–72 h → STOP / IV-to-oral / change / continue / OPAT.
- Hartford nomogram (aminoglycosides) — single daily dose 5–7 mg/kg (7 at RFH); level 6–14 h after dose; interval Q24 / Q36 / Q48.
- Egyptian schedule — BCG birth; OPV birth/2/4/6/9/18 mo; DTwP 2/4/6/18 mo; Hep B 2/4/6 mo; MMR 12/18 mo; MenAC 3/6/12/15 y.
- UK schedule — 5-in-1 (DTaP/IPV/Hib) at 2/3/4 mo; MMR 1st at 13 mo, 2nd at 3–5 y; Td/IPV at 13–18 y; HPV boys+girls 12–13 y.
Discriminators that decide questions
- Cerebral toxoplasmosis vs Primary CNS lymphoma — Toxo = multiple ring-enhancing lesions + serum anti-Toxoplasma IgG, headache a constant finding. Lymphoma = solitary lesion + CSF EBV, EBV-associated diffuse large B-cell.
- CMV vs EBV mononucleosis — CMV = mononucleosis without pharyngeal exudate or heterophile antibodies. EBV = tonsillitis + exudate + positive Monospot (heterophile antibody).
- Malaria relapse vs recrudescence — Relapse = P. vivax/ovale from dormant hypnozoites (needs primaquine). Recrudescence = P. falciparum from partial/incomplete treatment.
- Bacterial vs viral meningitis (CSF) — Bacterial = turbid, ≥1000 PMN, low glucose, raised LDH. Viral = clear, <100 lymphocytes, normal glucose, LDH not raised.
- OPV (Sabin) vs IPV (Salk) — OPV Sabin = live attenuated polio (may revert to wild-type, CI in immunosuppression/pregnancy). IPV Salk = killed polio (safe in immunocompromised).