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Dengue Fever — Preventive & Social Medicine (PSM)

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1. Introduction

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2. Causative Agent

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3. Epidemiology

3.1 Global Distribution

• Endemic across tropical and subtropical belt: South Asia, Southeast Asia, Latin America, Caribbean, sub-Saharan Africa, Pacific Islands
• Local autochthonous transmission reported in southern Europe (France, Italy, Spain)
• Historically endemic in Indian subcontinent, especially during post-monsoon months (August–November)

3.2 Host

• All ages susceptible, but highest attack rates in adolescents and young adults
• Highest risk of severe disease: infants, pregnant women, patients with comorbidities (asthma, sickle cell anemia, diabetes), and those with prior heterologous serotype infection

3.3 Agent Factors

• Immunity: Infection with one serotype confers lifelong homologous immunity and short-term cross-protection (1–3 years) against other serotypes. A person can have up to 4 dengue infections in a lifetime.
• Asymptomatic infection: ~75% of infections are asymptomatic; only ~25% are symptomatic

3.4 Reservoir

• Humans are the main amplifying reservoir (urban cycle)
• A sylvatic non-human primate cycle exists in Africa and Southeast Asia but rarely crosses to humans

3.5 Transmission

3.6 Vector (Aedes aegypti)

• Day-biting mosquito (peak biting: early morning and late afternoon)
• Peridomestic breeder — lays eggs in small collections of stagnant water (flower pots, tyres, coolers, uncovered tanks, even bolt-hole indentations)
• Extrinsic incubation period (in mosquito): 8–12 days; mosquito remains infective for life thereafter
• Highly associated with: water storage practices, poor sanitation, overcrowding, lack of screens/air conditioning

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4. Incubation Period

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5. Clinical Classification (WHO 2009)

Phase Progression

5.1 Dengue Without Warning Signs

• Fever + ≥2 of: nausea/vomiting, rash, aches/pains (myalgia, arthralgia, retro-orbital pain — "breakbone fever"), leukopenia, positive tourniquet test

5.2 Dengue With Warning Signs

• Abdominal pain or tenderness
• Persistent vomiting
• Clinical fluid accumulation (ascites, pleural effusion)
• Mucosal bleeding
• Lethargy/restlessness
• Liver enlargement >2 cm

5.3 Severe Dengue (DHF/DSS)

• Severe plasma leakage → shock (DSS) or respiratory distress
• Severe bleeding
• Severe organ involvement: AST/ALT ≥1000 IU/L, impaired consciousness, organ failure

The Hess/Tourniquet test (positive = >20 petechiae per square inch after inflating BP cuff to mean arterial pressure for 5 minutes) is a simple bedside capillary fragility test used in resource-limited settings.

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6. Diagnosis

• Combined NS1 + IgM on a single specimen (first 10 days) identifies ≥90% of cases
• IgM may cross-react with Zika, West Nile, Japanese encephalitis, yellow fever
• Dengue became a nationally notifiable disease in the US in 2010; suspected cases should be reported to local/state health departments

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7. Management (PSM Perspective — Supportive)

• No specific antiviral exists
• Avoid: Aspirin, NSAIDs (ibuprofen) — increase bleeding risk
• Febrile phase: paracetamol, adequate oral hydration
• Critical phase: close monitoring for shock signs (rising hematocrit, falling platelet count, fluid accumulation); IV crystalloids first; colloids/blood products for refractory shock
• Early recognition of shock reduces case fatality from 5–10% → <1%
• Hospital isolation: Standard precautions; vector control around infected patients to prevent transmission

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8. Prevention and Control (Core PSM Focus)

8.1 Vector Control (Most Important Public Health Measure)

Even Singapore — with stringent surveillance, screened windows, air conditioning, public health mosquito police, and fines for breeding sites — cannot fully prevent outbreaks, highlighting the difficulty of eliminating all peridomestic breeding opportunities.

8.2 Personal Protection

• Mosquito repellents containing DEET (EPA-registered)
• Long-sleeved clothing, especially during peak biting hours
• Screened windows, air-conditioned accommodation
• Bed nets (for children sleeping during day)
• Permethrin-treated clothing

8.3 Vaccination — Dengvaxia (CYD-TDV)

WHO (2018 revised guidance): Pre-vaccination screening is mandatory. Vaccinating dengue-naïve individuals is contraindicated.

8.4 Health Education and Community Participation

• "5-S" campaigns (Singapore model): Search, Spray, Stagnant water, Self-protection, Seek early treatment
• Community mobilization for weekly source reduction ("Dry Day")
• School programs and IEC (Information, Education, Communication) materials
• Inter-sectoral coordination: health, municipal, water supply departments

8.5 Surveillance

• Passive surveillance: Mandatory notification of all suspected/confirmed cases
• Active surveillance: Fever clinics, sentinel sites
• Entomological surveillance: Stegomyia (Breteau) index, House index, Container index to assess vector density
  • Breteau Index (BI): Number of positive containers per 100 houses — BI >5 signals outbreak risk
• Serological surveillance: Track serotype circulation, seroprevalence in population

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9. Outbreak Response

1. Verify outbreak — laboratory confirmation
2. Case search — active house-to-house survey
3. Vector control — emergency fogging + source reduction in affected area
4. Case management — identify/refer severe cases
5. Health communication — community mobilization, media briefings
6. Entomological investigation — identify breeding sites
7. Report to higher authorities — WHO IHR 2005 reporting (dengue is monitored as a public health event of potential international concern)

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10. Epidemiological Indices for Dengue Vector (Ae. aegypti)

BI is the most epidemiologically informative index.

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11. Key PSM Points to Remember

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