Epidemiology, Prevention, Control and Management of Water-Borne Diseases

1. Definition and Classification

2. Global Epidemiology

Burden of Disease

• WBDs account for an estimated 3.6% of the total global disability-adjusted life year (DALY) burden (WHO)
• Approximately 1.5 million deaths annually are attributable to WBDs
• Diarrheal disease is the second leading cause of death in children under 5 years globally
• Children under 3 years in low-income countries experience an average of 3 episodes of diarrhea annually
• Poor WASH (Water, Sanitation, Hygiene) conditions account for >1 million diarrheal deaths every year (WHO)

Geographic Distribution

• High prevalence in low- and middle-income countries in tropical and subtropical regions (sub-Saharan Africa, South Asia, Southeast Asia)
• Major etiological agents in LMICs: Rotavirus and E. coli (most common); Shigella and Cryptosporidium are also globally significant
• In the US, Cryptosporidium is the most common cause of recreational waterborne GI illness (CDC estimates ~748,000 cases/year)

Relationship with Rainfall and Climate

• Reviews of waterborne outbreaks in the US found 51% were preceded by precipitation levels above the 90th percentile (Harrison's Principles of Internal Medicine, 22nd Ed.)
• Surface water contamination outbreaks typically occur within 1 month of a heavy precipitation event; groundwater contamination outbreaks tend to occur 2+ months later
• Vibrio and Leptospira species are the pathogens most commonly involved following heavy precipitation
• Climate change is expanding the range and seasonality of waterborne outbreaks - warming temperatures favor Vibrio proliferation

Combined Sewer Systems

• Roughly 40 million people in the US (and millions more globally) rely on combined sewer systems that carry stormwater and sewage in the same pipe
• These systems, designed in the 19th century, are increasingly overwhelmed by modern heavy rainfall events, leading to sewage overflows into freshwater bodies with E. coli levels up to 100x the EPA guidance for recreational water

Historical Significance

• John Snow's investigation of the 1854 Broad Street cholera outbreak in London provided the first epidemiological evidence of water's role in cholera transmission
• William Budd similarly documented typhoid transmission through polluted drinking water (1856)

3. Epidemiological Triad

4. Prevention Strategies

A. Primary Prevention (Preventing Exposure)

• Chlorination - the most widely used and cost-effective water disinfection method
• Boiling - effective household-level treatment (destroys all pathogens)
• Solar disinfection (SODIS) - exposure of water in PET bottles to sunlight for 6+ hours
• Filtration - ceramic, biosand, membrane filters
• UV irradiation - effective against protozoa (e.g., Cryptosporidium) that are chlorine-resistant
• Coagulation-flocculation-sedimentation - removes turbidity and pathogens
• Safe household water storage in covered containers

• Construction and use of proper latrines/toilets
• Sewage treatment before discharge
• Separation of drinking water sources from fecal waste disposal
• Open defecation-free (ODF) communities

• Regular handwashing with soap, especially before eating and after defecation
• Food hygiene (washing produce, cooking food thoroughly)
• Proper disposal of human waste

• Oral Cholera Vaccine (OCV) - WHO recommends in endemic areas and outbreaks; included in routine childhood vaccination in many countries
• Typhoid conjugate vaccine (TCV) - recommended for travelers and endemic area populations; superior to older Vi polysaccharide vaccine
• Hepatitis A vaccine - recommended for travelers and high-risk groups
• Polio vaccine (OPV/IPV) - part of EPI schedules

• Water quality monitoring at source, treatment, and point-of-use
• Disease surveillance systems for early outbreak detection
• Environmental monitoring (sentinel sites)

B. Secondary Prevention (Early Detection and Treatment)

• Rapid case detection through surveillance
• Stool culture and sensitivity testing
• Prompt oral rehydration therapy (ORT) for diarrheal diseases
• Contact tracing during outbreaks
• Isolation of cases (especially for cholera, typhoid)

C. Tertiary Prevention

• Management of complications (septicemia, perforation in typhoid, cholera shock)
• Nutritional rehabilitation after illness
• Rehabilitation of chronic sequelae (e.g., reactive arthritis after enteric infections)

5. Control Measures

Source Control

• Protection of water sources: fencing wells, covering springs, preventing animal access to water sources
• Watershed protection: preventing agricultural runoff, industrial effluents, and open defecation near water bodies
• Groundwater protection: proper well construction with sealed casings, drainage aprons, and minimum separation from latrines (30 meters)

Water Treatment (Municipal Level)

1. Screening/Straining - removes large debris
2. Coagulation and Flocculation - chemical agents (alum) cause particles to clump
3. Sedimentation - settling of flocculated particles
4. Filtration - slow sand filtration or rapid sand filtration
5. Disinfection - chlorination (free residual chlorine 0.2-0.5 mg/L at point of delivery), ozonation, UV
6. pH adjustment and fluoridation - where appropriate

Point-of-Use Treatment (Household Level)

• Boiling, chlorine tablets, ceramic water filters, SODIS, safe storage
• WHO's "3-glass model": source protection + treatment + safe storage

Outbreak Control

• Identification and elimination of the contaminated source
• Boil-water advisories
• Mass ORS distribution
• Emergency chlorination
• Case isolation and treatment
• Health education campaigns
• Epidemiological investigation (case-counting, vehicle identification)

Environmental Control

• Proper sewage disposal and wastewater treatment
• Fly control (flies transfer pathogens from feces to food/water)
• Rodent control
• Solid waste management to prevent contamination of water bodies

6. Clinical Management of Key Water-Borne Diseases

Cholera

• Mainstay: Oral rehydration solution (ORS) - WHO standard formula
• Severe cases: IV fluids (Ringer's lactate), rapid correction of dehydration
• Antibiotics (shorten duration): Doxycycline (single dose, adults), Azithromycin (children, pregnant women), Ciprofloxacin
• Zinc supplementation in children (reduces duration and severity)

Typhoid Fever

• First-line: Fluoroquinolones (Ciprofloxacin) for susceptible strains; increasingly Azithromycin or Ceftriaxone for drug-resistant strains
• MDR/XDR typhoid: Carbapenems may be required
• Supportive care: antipyretics, fluids, nutrition
• Complications: Intestinal perforation requires surgical management

Hepatitis A

• Supportive treatment; no specific antiviral
• Rest, avoid hepatotoxic drugs and alcohol

Cryptosporidiosis

• Nitazoxanide (immunocompetent patients)
• Supportive ORT for diarrhea
• Immunocompromised patients (HIV): ART to restore immune function

Amoebiasis

• Tissue amoebiasis: Metronidazole or Tinidazole
• Luminal cysts: Diloxanide furoate or Paromomycin (to prevent carrier state)

7. National and International Programmes

India

International / Global

8. Surveillance

• Case-based surveillance: mandatory reporting of notifiable diseases (cholera, typhoid, hepatitis A)
• Outbreak surveillance: investigation of disease clusters linked to common water source
• Water quality monitoring: regular bacteriological (coliform counts) and chemical testing
• Sentinel surveillance: health facility-based monitoring of diarrheal disease trends
• Event-based surveillance (EBS): media monitoring, community alerts, rumor tracking

9. WHO Water Safety Plan Framework

1. System Assessment - identify hazards and risks throughout the supply chain (catchment to consumer)
2. Operational Monitoring - control measures with defined critical limits
3. Management Plans - documentation, verification, and response

10. Key Indicators for Control