Infectious Diseases and Tropical Medicine
Core concepts
Sepsis is infection with organ dysfunction: cultures, lactate, antibiotics within an hour and fluid resuscitation. HIV: serology has a window period; CD4 count drives prophylaxis (co-trimoxazole under 200, azithromycin for Mycobacterium avium under 50); know the opportunistic infections (Pneumocystis pneumonia, toxoplasmosis, cryptococcal meningitis, CMV retinitis, Kaposi's sarcoma) and post-exposure prophylaxis within 72 hours. Tuberculosis: latent (IGRA or Mantoux) versus active (sputum microscopy, culture, PCR); reactivation risk with anti-TNF therapy and immunosuppression. Meningitis: cerebrospinal fluid interpretation - bacterial (neutrophils, high protein, low glucose), viral (lymphocytes, normal glucose), tuberculous (lymphocytes, very high protein, low glucose), cryptococcal antigen. Malaria: falciparum (severe disease, cerebral malaria, hypoglycaemia, blackwater fever) treated with artesunate; vivax and ovale need chloroquine plus primaquine for hypnozoites after G6PD testing. Diarrhoea: invasive (blood, pus, fever) versus toxin-mediated; amoebic (flask ulcers, liver abscess) versus bacillary dysentery. Endocarditis: modified Duke criteria, three blood culture sets before antibiotics, echocardiography. Needlestick injury: wash, risk assess, HIV and hepatitis B prophylaxis.
Traps
Delaying antibiotics to obtain cultures in a shocked patient. Assuming a normal CSF glucose excludes tuberculous meningitis. Relying on a single negative HIV test in the window period. Giving primaquine without checking G6PD status.
Rule of thumb
Aseptic meningitis with a very high CSF protein and low glucose suggests TB or fungal disease; a CD4 count below 200 with dry cough and hypoxia suggests Pneumocystis - treat with high-dose co-trimoxazole plus steroids if hypoxic.