Learn — Environmental, occupational & school health

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Airborne, droplet, contact precautions

Transmission-based precautions are the second tier of infection prevention, applied as airborne, droplet or contact precautions to a patient with a known or suspected infection, in addition to the standard precautions that are applied to every patient all of the time. They matter because the precaution has to be chosen from the route of spread and started on suspicion, since a ward is exposed during the two days spent waiting for a laboratory report.

Standard precautions apply to every patient regardless of diagnosis and cover hand hygiene at the WHO five moments, gloves for contact with blood, body fluids, mucous membranes and non-intact skin, gown and eye protection where splashing is likely, safe injection practice with no recapping of needles, disposal of sharps at the point of use, respiratory hygiene and cough etiquette, safe handling of linen and equipment, and correct biomedical waste segregation.
Airborne precautions are for agents carried in droplet nuclei smaller than 5 micrometres that stay suspended and travel on air currents, namely pulmonary and laryngeal tuberculosis, measles, chickenpox and disseminated zoster: the patient goes into an airborne infection isolation room at negative pressure with 6 to 12 air changes an hour, or in an Indian primary care setting a well-ventilated single room with the windows open and the door shut, everyone entering wears a fit-checked N95 respirator, and the patient wears a surgical mask whenever he leaves the room.
Droplet precautions are for larger particles over 5 micrometres that fall within about one to two metres, namely influenza, COVID-19, pertussis, mumps, rubella, diphtheria, meningococcal disease, group A streptococcal pharyngitis and Haemophilus influenzae type b disease: a single room or cohorting with at least one metre between beds, a surgical mask for anyone working within a metre, and a mask on the patient during transport, with no special air handling needed.
Contact precautions are for spread by touch or by contaminated surfaces, namely MRSA, VRE, Clostridioides difficile, multidrug-resistant gram-negative organisms, scabies, lice, respiratory syncytial virus, rotavirus, impetigo and draining wounds: gown and gloves are put on before entering the room, equipment such as the stethoscope, thermometer and blood pressure cuff is dedicated to the patient, and surfaces are disinfected.
Some infections need two categories together: COVID-19 needs droplet and contact precautions with airborne precautions added during aerosol-generating procedures such as suction, intubation, nebulisation, non-invasive ventilation and bronchoscopy, and disseminated varicella-zoster needs airborne and contact precautions.
The order of donning and doffing matters because most self-contamination occurs while removing equipment: put on gown, then respirator or mask, then eye protection, then gloves; remove gloves, then eye protection, then gown, and remove the respirator last and outside the room, performing hand hygiene between the steps.
Biomedical waste in India is segregated at the point of generation under the 2016 rules: yellow for anatomical, soiled and infectious waste which is incinerated, red for contaminated recyclable plastics, a white translucent puncture-proof container for sharps, and blue for glassware and metallic implants; needles are never recapped and a sharps container is never filled beyond about three-quarters.
Isolation applies to a case for the period of communicability while quarantine applies to a healthy exposed contact for the maximum incubation period, and alcohol-based hand rub is the default for hand hygiene except when the hands are visibly soiled or the organism is a spore former, when soap and running water are required.

Hardness of water

Hardness is the soap-destroying power of water, caused mainly by dissolved calcium and magnesium salts and reported as milligrams per litre of calcium carbonate equivalent. It matters in public health practice because hard water wastes soap and fuel, scales pipes and boilers, makes pulses and vegetables refuse to soften, and because the base-exchange softening used to correct it adds sodium to the water — while hardness itself has never been shown to cause disease.

Temporary or carbonate hardness is due to the bicarbonates of calcium and magnesium and is removed by boiling, which drives off carbon dioxide and precipitates the carbonate, or by adding lime in Clark's process.
Permanent or non-carbonate hardness is due to the sulphates, chlorides and nitrates of calcium and magnesium, is not removed by boiling, and is dealt with by the base-exchange or ion-exchange (zeolite) process, by adding sodium carbonate, or by reverse osmosis.
The usual classification as calcium carbonate is soft below 75 mg/L, moderately hard 75 to 150 mg/L, hard 150 to 300 mg/L and very hard above 300 mg/L; hardness is measured in the laboratory by EDTA titration, and the old unit of one degree Clark equals one grain of calcium carbonate per gallon, or 14.25 mg/L.
The Indian drinking water specification IS 10500 sets total hardness at an acceptable limit of 200 mg/L as calcium carbonate and a permissible limit of 600 mg/L where no alternative source is available, so a hard supply is a nuisance to be corrected rather than a supply to be condemned.
Water softened by base exchange has its calcium and magnesium replaced by sodium, which is worth knowing for a patient on salt restriction, on dialysis or with heart failure; very soft and acidic water is corrosive and dissolves metal from pipes.
Hardness is only one of the standards the nurse should be able to quote alongside it: water must also be clear, with a pH between 6.5 and 8.5, a fluoride content within the acceptable limit of 1.0 mg/L and permissible limit of 1.5 mg/L, and a free residual chlorine that shows disinfection has worked — and none of these substitutes for bacteriological testing.

Chlorination

Chlorination is the addition of chlorine to water to kill pathogenic organisms, and it is the single most important safeguard against water-borne disease as well as the one measure the community health nurse can supervise herself at village level. It supplements but never replaces filtration and sedimentation, because chlorine acts on organisms and not on turbidity: water must be clear before it is chlorinated, or the dose is wasted on suspended matter and the organisms sheltering in it.

Chlorine added to water hydrolyses to hypochlorous acid and the hypochlorite ion; hypochlorous acid is the active germicide, and because it predominates in acid and neutral water, disinfection works best at a pH below 8 and poorly in highly alkaline water.
Chlorine demand is the amount consumed by organic matter, ammonia, iron, manganese and bacteria; break-point chlorination is the point at which that demand has been satisfied and any further chlorine appears as free residual chlorine, which is the fraction that matters.
The standard of safety is a free residual chlorine of 0.5 mg/L after a contact period of at least one hour in clear water; the residual is read in the field with a chlorometer using DPD, the older test being orthotolidine, and the Bureau of Indian Standards asks for a minimum of 0.2 mg/L at the consumer's tap.
Bleaching powder (calcium hypochlorite) contains about 33 per cent available chlorine when fresh but loses strength rapidly in a damp, warm or open container, so it is stored in a closed, dark, cool, dry tin and the available chlorine is rechecked before a dosing campaign; the alternatives are stabilised bleaching powder, high-test hypochlorite, one per cent sodium hypochlorite solution for household use, chlorine tablets for individual use and chlorine gas at treatment plants.
To disinfect a dug well, the volume of water is worked out from the area of the well and the depth of the water column, the bleaching powder is made into a paste and then a slurry, mixed thoroughly through the water column with a bucket, left for one hour and then tested for residual chlorine; the Horrocks apparatus is the field method for finding how much bleaching powder that particular well needs, and dosing is repeated weekly and after every heavy rain.
Superchlorination followed by dechlorination with sodium thiosulphate is used for grossly polluted water, and during a cholera or acute diarrhoeal disease outbreak the residual is deliberately kept above the routine level and the wells are dosed more often.
Know what chlorine does not do: at ordinary doses it does not kill the cysts of Entamoeba histolytica and Giardia, helminth ova or Cryptosporidium oocysts, it needs higher doses and longer contact for some viruses, and where it meets a lot of organic matter it forms trihalomethanes and a taste that makes families abandon the treated supply.

Air pollution indices

An air quality index converts the measured concentrations of several pollutants into a single number, colour and word so that the public can be told in one phrase how dangerous the day's air is. India's National Air Quality Index, launched by the Central Pollution Control Board in 2015 under the slogan of one number, one colour, one description, is the index examined here, and the nurse uses its category to decide what to tell people with asthma, chronic obstructive pulmonary disease and heart disease, and what to tell pregnant women, children and the elderly.

The Indian AQI has six categories: Good 0 to 50, Satisfactory 51 to 100, Moderately polluted 101 to 200, Poor 201 to 300, Very poor 301 to 400 and Severe 401 to 500, coloured from dark green through yellow and orange to red and dark red.
Eight pollutants are used — PM10, PM2.5, nitrogen dioxide, sulphur dioxide, carbon monoxide, ozone, ammonia and lead — the index is the worst of their individual sub-indices, and at least three pollutants must be measured, one of which must be PM10 or PM2.5.
The National Ambient Air Quality Standards of 2009 set PM2.5 at 40 micrograms per cubic metre as an annual mean and 60 over 24 hours, and PM10 at 60 annual and 100 over 24 hours; the WHO global air quality guidelines of 2021 are far stricter at 5 micrograms per cubic metre annual and 15 over 24 hours for PM2.5.
PM2.5 is the fraction that matters most because it reaches the alveoli and enters the blood, causing not only asthma and COPD exacerbations but also myocardial infarction, stroke, low birth weight and lung cancer; the older indices in the textbooks, such as smoke density read against the Ringelmann chart and combined smoke and sulphur dioxide indices, measure the coarse pollution of an earlier era.
Indoor air pollution from biomass cooking fuel is the exposure that dominates rural India and falls on women and small children, causing acute respiratory infection in the under-fives and chronic obstructive lung disease in women who have never smoked; the programme answer is the LPG connection under the Pradhan Mantri Ujjwala Yojana, improved stoves, a smoke hood and a ventilated kitchen.
The National Clean Air Programme, launched in 2019 by the Ministry of Environment, Forest and Climate Change, covers more than 130 non-attainment cities and set a target reduction in particulate concentrations against a 2017 baseline, later revised upward in both ambition and deadline; Delhi and the National Capital Region additionally run a Graded Response Action Plan whose stages are triggered by the AQI band.
Health advice by band is what the nurse actually gives: at Poor and above, sensitive groups avoid prolonged outdoor exertion; at Very poor and Severe everyone stops outdoor exercise, schools move activity indoors, windows are kept shut during the morning and evening peaks, and only an N95 or FFP2 respirator helps, because cloth and surgical masks do not filter PM2.5.

Occupational hazards

Occupational hazards are the physical, chemical, biological, mechanical and psychosocial exposures at work that cause disease, injury or death, and occupational health is the branch of public health that adapts the work to the worker and the worker to his job. It matters in India because the great majority of the workforce is in the unorganised sector, outside factory inspection and outside insurance, so the community health nurse is often the only person who ever connects a stone crusher's cough, a farmer's pinpoint pupils or a health worker's needle-stick to the work that caused it.

Physical hazards: heat, causing heat cramps, heat exhaustion and heat stroke; cold; noise, where the Indian permissible limit is 90 decibels for an eight-hour working day and the earliest loss on the audiogram is a dip at 4,000 Hz; segmental vibration causing white finger; ionising and ultraviolet radiation; and poor illumination.
Chemical hazards: lead, producing colic, wrist drop, a blue Burtonian line on the gums, punctate basophilia and anaemia; mercury with tremor, gingivitis and erethism; arsenic, cadmium and manganese; benzene causing aplastic anaemia and leukaemia; and organophosphate insecticides in agricultural workers.
The pneumoconioses are the classic examination material: silicosis from free silica in quarrying, stone crushing, sandblasting, slate pencil and agate work, with upper-zone nodules and eggshell calcification of the hilar nodes; asbestosis with pleural plaques, bronchogenic carcinoma and mesothelioma; byssinosis from cotton dust, worst on the first day back at work; bagassosis from sugarcane waste; farmer's lung from mouldy hay; and anthracosis in coal workers.
Silicosis is irreversible and has no specific treatment, so removal from exposure is the whole of management, and every silicotic must be screened for tuberculosis, because silica cripples the alveolar macrophage and silicotuberculosis is common.
Biological hazards fall on two groups: agricultural workers, with anthrax, brucellosis, leptospirosis, tetanus and hydatid disease; and health-care workers, with tuberculosis, hepatitis B and C and HIV from needle-stick and splash injuries — which is why hepatitis B vaccination of staff, sharps containers and the no-recapping rule are occupational health measures and not merely infection control.
Ergonomic and psychosocial hazards — lifting injuries and low back pain, repetitive strain, machinery injury, falls, shift work, burnout and workplace violence — account for far more lost days than the exotic poisonings, and they are the ones nurses themselves suffer.
The statutory frame is the Factories Act 1948 (health, safety, welfare, creche facilities and the notification of listed occupational diseases), the Employees' State Insurance Act 1948, the Mines Act, the Employees' Compensation Act 1923, the Building and Other Construction Workers Act 1996 and the Occupational Safety, Health and Working Conditions Code 2020, which consolidates the earlier labour laws; the ESI scheme covers employees below a monthly wage ceiling of Rs 21,000 and provides medical, sickness, maternity, disablement, dependants' and funeral benefits, financed by employer and employee contributions.
Control follows a hierarchy and personal protective equipment comes last: eliminate or substitute the hazardous material, then engineer it out with enclosure, local exhaust ventilation and wet drilling, then use administrative controls such as job rotation, exposure limits, pre-placement and periodic medical examination and training, and only then rely on the respirator, which depends on a tired worker wearing it correctly all day.

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