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Answers from K. Park's Textbook of Preventive and Social Medicine

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1. What is Safe Drinking Water?

I. Acceptability Aspects (Physical Parameters)

• Turbidity: Should not exceed 4 NTU (nephelometric turbidity units). For effective disinfection, median turbidity should be ≤1 NTU.
• Colour: ≤ 15 TCU (true colour units)
• Taste and odour: Should be acceptable - no health-based guideline value, but unusual taste/odour may indicate harmful substances
• Temperature: Cool water is more palatable; no guideline value is set

II. Chemical Standards (Key limits)

III. Microbiological Standards

• The coliform group is the primary bacterial indicator of water safety
• E. coli (faecal coliform) is the key indicator of faecal pollution
• Drinking water should ideally contain zero coliform organisms
• Supplementary indicators: faecal streptococci and sulphite-reducing clostridia
• The coliform organisms are defined as: aerobic and facultative anaerobic, gram-negative, non-sporing rods that ferment lactose at 35-37°C within 48 hours

IV. Radiological Aspects

"The purpose of standards is to minimise all the known health hazards." - Park's, Water Quality chapter

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2. How is the Iodine Content in Salt Tested?

A. Field/Spot Test (Qualitative) - Most Commonly Described

• Principle: Iodine reacts with starch to give a blue-purple colour
• Method: A few drops of starch solution (or freshly cut potato/cooked rice) are placed on salt, followed by a drop of dilute acid (acidified starch-iodide paper/WYD iodine testing kit)
• A blue-purple colour indicates the presence of iodine in salt
• This is the field-level test used by ASHA workers, anganwadi workers, and field supervisors under NIDDCP

B. Semi-Quantitative Test - Rapid Test Kit (RTK)

• Based on the starch-iodine reaction - intensity of blue colour corresponds to iodine concentration
• The RTK can detect iodine in the range of officially recommended levels (15 ppm = 15 mg iodine/kg salt)
• Results are interpreted by comparing colour against a reference chart

C. Quantitative Method - Iodometric Titration

• Used in laboratories: based on the thiosulfate-starch reaction
• Reference standard method to accurately estimate iodine content in ppm

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3. What Investigations are Done for Fever Under NVBDCP?

A. Blood Smear Examination (Microscopy)

• Active Case Detection (ACD): Blood smears are collected from fever cases by MPWs/ANMs during fortnightly house visits in rural areas
• Passive Case Detection (PCD): Done in fever cases reporting to peripheral health volunteers/ASHAs, sub-centres, malaria clinics, CHCs, PHCs, and other health institutions
• Microscopy remains the gold standard - it has high sensitivity and specificity and is more economical
• About 100 million blood slides are collected from fever cases in India annually, detecting approximately 1.5 million malaria cases

B. Rapid Diagnostic Tests (RDTs)

• Introduced in 2003 by NVBDCP for early diagnosis of malaria
• Bivalent RDTs (detect both P. vivax and P. falciparum) introduced in 2012
• Provided to community-level ASHA workers and other volunteers for timely diagnosis in remote/tribal areas
• In many areas, RDTs are now the established method of choice

C. Type of RDT Used:

1. Monovalent RDT - detects P. falciparum only
2. Bivalent RDT - detects both P. vivax and P. falciparum

D. When Both Methods are Unavailable:

• Trained workers at PHC level do blood smear examination
• In villages where no ASHA/volunteer is deployed, MPWs perform ACD

Surveillance Parameters Monitored:

• (a) Annual Parasite Incidence (API)
• (b) Annual Blood Examination Rate (ABER) - maintained at ~10%
• (c) Annual Falciparum Incidence (AFI)
• (d) Slide Positivity Rate (SPR)
• (e) Slide Falciparum Rate (SFR)

All fever cases diagnosed as malaria by either RDT or microscopy should be promptly given effective treatment - Park's NVBDCP chapter

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4. How are Source Reduction Activities Done?

Methods by Mosquito Type:

Specific Activities:

1. Filling and levelling - Fill low-lying areas, pits, ditches
2. Drainage - Drain stagnant water; maintain drainage channels
3. Water management - Intermittent irrigation (periodic drying of rice fields interrupts breeding)
4. Changing water salinity - Renders water unsuitable for mosquito breeding
5. Deepening or flushing water bodies
6. Removal of aquatic vegetation - For Mansonia control (pistia plants)
7. Peri-domestic sanitation - Eliminating breeding near homes
8. Social participation - Community involvement in keeping environment clean

"Source reduction methods generally produce results that are permanent." - Park's

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5. Insecticides Used in Spraying and Fogging

A. Residual Spraying (Indoor Residual Spray - IRS)

• DDT is the insecticide of choice under NVBDCP; alternatives used where DDT resistance has developed
• Two rounds of DDT/synthetic pyrethroids per transmission season
• Three rounds of malathion required per season
• About 60% of high-risk areas under IRS use DDT

B. Space Sprays / Fogging

1. Pyrethrum extract (Pyrethrin)
   • Dosage: 1 oz of 0.1% pyrethrin solution per 1,000 cubic feet
   • Doors and windows closed for 30 minutes after spraying
   • Excellent contact poison - kills instantly; no residual action
   • Useful for domestic and temporary personal protection
2. Malathion - Used for ULV (Ultra Low Volume) fogging
3. Fenitrothion - Also used for ULV fogging

"The most extensively used insecticides are malathion and fenitrothion for ULV fogging." - Park's, Mosquito Control chapter

• Park's Textbook of Preventive and Social Medicine, Water Quality chapter (p. 819-821)
• Park's Textbook of Preventive and Social Medicine, NVBDCP/Malaria chapter (p. 302, 473-474)
• Park's Textbook of Preventive and Social Medicine, Mosquito Control chapter (p. various)