Leptospirosis and dengue in the older adult

Why these matter in the elderly (textbook principle). Both are monsoon-season febrile illnesses that are highly prevalent in India. Older adults have higher morbidity and mortality because the febrile response is blunted or absent, symptoms are under-reported, coexisting disease masks acute infection, and acute unexplained functional deterioration or confusion may be the only presenting feature. Absence of fever or leucocytosis does not exclude serious infection.

Dengue — clinical. WHO classification: dengue without warning signs; dengue with warning signs (abdominal pain or tenderness, persistent vomiting, clinical fluid accumulation, mucosal bleeding, lethargy or restlessness, liver enlargement >2 cm, rising haematocrit with rapidly falling platelets); and severe dengue (shock, severe bleeding, severe organ impairment). Older adults less often show the classical rash and retro-orbital pain and more often present with "expanded dengue syndrome" — encephalopathy, myocarditis, acute kidney injury, hepatitis and decompensation of existing heart failure or diabetes.

Dengue — diagnosis. NS1 antigen (days 1–5), IgM ELISA (after day 5), RT-PCR where available; serial CBC (thrombocytopenia with rising haematocrit), liver and renal function, ECG. Geriatric pitfall: baseline anaemia, chronic kidney disease and diuretic therapy make haematocrit an unreliable marker of plasma leakage — a "normal" haematocrit may already represent significant haemoconcentration.

Dengue — management. No antiviral exists; treatment is careful fluid replacement. Use weight-based crystalloids titrated to haematocrit, urine output and haemodynamics, with far tighter monitoring in the elderly because the window between hypovolaemia and iatrogenic fluid overload / pulmonary oedema is very narrow. Paracetamol only — avoid NSAIDs and aspirin (bleeding and acute kidney injury). Platelet transfusion only for clinically significant bleeding, never for a platelet number alone. Withhold antiplatelets and anticoagulants during the thrombocytopenic phase and restart deliberately — a key geriatric decision.

Leptospirosis — clinical. Zoonosis from rodent urine and floodwater; risk in farmers, paddy workers and those wading through contaminated water — heavily represented in older rural and coastal populations (Kerala, Tamil Nadu, Gujarat, Andaman). Classically biphasic: a septicaemic phase (abrupt fever, severe myalgia especially of the calves, conjunctival suffusion, headache) followed by an immune phase. Severe forms: Weil's disease (jaundice + acute kidney injury + haemorrhage), pulmonary haemorrhage syndrome (highest mortality), myocarditis and aseptic meningitis.

Leptospirosis — diagnosis and treatment. Microscopic agglutination test (MAT) is the reference standard; IgM ELISA / rapid tests for early diagnosis; blood culture in the first week and urine culture in the second; PCR. Mild disease — doxycycline 100 mg twice daily for 7 days. Severe disease — IV penicillin G or ceftriaxone 1– 2 g daily. Watch for the Jarisch–Herxheimer reaction. Supportive care is decisive: early dialysis for AKI improves survival, and ventilatory support for pulmonary haemorrhage.

India's first dengue vaccine was approved on 21 July 2026: the DCGI granted marketing authorisation to TAK-003 (Qdenga), a live-attenuated tetravalent vaccine given as two doses three months apart, without pre-vaccination screening — but licensed only for ages 4–60 years, so it does not currently cover the older adult population, in whom vector control, early recognition and meticulous fluid management remain the only strategy. (TAK-003 was WHO-prequalified in May 2024; 7-year TIDES data show ~84% efficacy against hospitalised dengue. India's indigenous single-dose candidate DengiAll — ICMR/Panacea Biotec — is in Phase 3.) For leptospirosis, current NCVBDC/ICMR practice supports presumptive doxycycline for acute undifferentiated febrile illness during monsoon in endemic districts, and doxycycline 200 mg weekly chemoprophylaxis for high-risk post-flood exposure, as used in Kerala's post-flood outbreak response. If this appears as a 15-mark question, add: a comparison table of dengue vs leptospirosis vs scrub typhus vs malaria in acute undifferentiated febrile illness (a favourite Indian examiner question — conjunctival suffusion and calf tenderness for lepto, eschar and doxycycline response for scrub typhus, thrombocytopenia with haemoconcentration for dengue); the dengue fluid algorithm by group A/B/C; criteria for ICU admission; the Faine's criteria for leptospirosis; complications of both in patients on RAAS blockers, diuretics, metformin and anticoagulants; and the role of the National Centre for Vector Borne Diseases Control (NCVBDC) programme.