The health impact of sanitation Sandy Cairncross Professor of Environmental Health London School of...

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The health impact of sanitation

Sandy CairncrossProfessor of Environmental Health

London School of Hygiene& Tropical Medicine

sandy.cairncross@lshtm.ac.uk

Health may be a major benefit, but it is not the main one in the eyes of the consumer.

Benefits of latrine to 320 households in rural Benin (Average importance rating, scale 1-4)

Avoid discomforts of the bush 3.98Gain prestige from visitors 3.96Avoid dangers at night 3.86Avoid snakes 3.85Reduce flies in compound 3.81Avoid risk of smelling/seeing faeces in bush 3.78Protect my faeces from enemies 3.71Have more privacy to defecate 3.67Keep my house/property clean 3.59Feel safer 3.56Save time 3.53Make my house more comfortable 3.50Reduce my household’s health care expenses 3.32Leave a legacy for my children 3.16Have more privacy for household affairs 3.00Make my life more modern 2.97Feel royal 2.75Make it easier to defecate due to age/sickness 2.62Be able to increase my tenants’ rent 1.17For health (spontaneous mention) 1.27

Source: Jenkins MW (1999) PhD thesis, UC Davis, Civil Engineering

Fewtrell et al. (2004) review:

“No study excluded on basis of quality alone”

Criteria for “good” studies:

• Adequate control group

• Clear measurement/control of confounders

• Diarrhoea outcome defined

• Recall period ≤ 2 weeks

NB Observational studies included

Previous reviews:

a – d Esrey SA et al. (1991) Bull WHO 69 (5): 609-621

e Curtis V, Cairncross S (2003) Lancet Inf Dis 3: 275-281.

(a) Sanitation (b) Wateravailability

(c) Waterquality

(d) Hygienepromotion

(e) Handwashing

Previous reviews Fewtrell et al. (2004)

Problems with systematic reviews:

• Confounding in observational studies

• No placebo in intervention studies

• Trade-off between quality and numbers

• Wide confidence intervals

• Who defines quality? “Judgement-free data” are a mirage

• Extrapolation from morbidity to mortality

• Publication bias

• Bottom-line impact figure obscures variation

Health impact

measurement; a

cautionary tale

Health impact measurement; a cautionary tale Village Piped water Dug hole

Namabengo 15/216 ( 7%)

Mkongo 39/134 (29%)

Children < 5 years with diarrhoea during previous week

Source: Prag JB et al. (1983) Water Master Plan for Iringa, Ruvuma and Mbeya Regions, Tanzania Vol. 13 Ch. 11.

Namabengo 15/216 ( 7%)

Mkongo 39/134 (29%)

Village Piped water Dug hole

Namabengo 4/216 (1.9%)

Mkongo 12/133 (9.0%)

Children < 5 years with positive Widal (S. typhi H antigen)

Namabengo 15/216 ( 7%) 5/70 ( 7%)

Mkongo 37/100 (37%) 39/134 (29%)

Namabengo 4/216 (1.9%) 1/70 (1.4%)

Mkongo 7/100 (7.0%) 12/133 (9.0%)

Namabengo:Higher altitude, cooler, less growth of faecal pathogens

Large mission hospital, handing out antimalarials

- and malaria causes immunosuppression

Away from the lake area, affected by a typhoid outbreak

Namabengo 15/216 ( 7%) 5/70 ( 7%)

Mkongo 37/100 (37%) 39/134 (29%)

Totals 52/316 (16%) 44/204 (22%)

Namabengo 4/216 (1.9%) 1/70 (1.4%)

Mkongo 7/100 (7.0%) 12/133 (9.0%)

Totals 11/316 (3.5%) 13/203 (6.4%)

Multivariate analysis is not guaranteed to

remove confounding, especially when

RR < 2

The Clofibrate study; 5-year mortality among at-risk men (%)

Group Compliance with treatment

Relative Risk

< 80% ≥ 80%

Clofibrate (N = 1103)

24.6 15.0 1.64 1.1 x 10-4

Placebo (N = 2789

28.2 15.1 1.87 4.7 x 10-16

Coronary Drug Project Research Group (1980) N. Engl. J. Med. 303: 1038-1041.

The Clofibrate study; 5-year mortality among at-risk men (%)

Group Compliance with treatment

Relative Risk

< 80% ≥ 80%

Clofibrate (N = 1103)

24.6 15.0 1.64 1.1 x 10-4

Placebo (N = 2789

28.2 15.1 1.87 4.7 x 10-16

After controlling for 40 potential confounding factors by multiple regression:

Placebo 25.8 16.4 1.57 7.3 x 10-9 Coronary Drug Project Research Group (1980) N. Engl. J. Med. 303: 1038-1041.

‘Determinants’ of good hand washing among 90 rural Bangladeshi women

Observed hand washingbehaviour after defecationGood Poor Rel. rate (95% CI)

Own sanitary latrine usedyes 22 11 1.73 (1.15-2.59)no 22 35

Owns agricultural landyes 36 24 2.25 (1.20-4.22)no 8 22

Believes that washing hands prevents diseases

yes 26 27 1.01 (0.66-1.55)no 21 18

Source: Hoque BA et al. (1995) Public Health 109: 15-24

Can television

protect you

from diarrhoea?

“Long-term longitudinal studies of large size and expense are probably the only means through which there is any chance of isolating a specific quantitative relationship between water supply and health… [Given] the very high cost, limited possibility of success and restricted application of results, [such studies should not be undertaken].”

Source: World Bank (1976) Measurement of the health benefits of investments in water supply. Report of an Expert Panel, Public Utilities Dept. Report no. PUN 20.

Conclusion:

Measuring health benefits is tricky; better to measure intermediate variables

-access

-time saving, cost reduction

-hygiene

Most sanitation health impact studies:

•are observational

(hence subject to confounding)

But also

•are in rural settings

•don’t allow for “mass effect”

•have a single disease outcome

Excreta-related infectionsDisease group Impact of sanitation

Non-bacterial faeco-oral Negligible

Bacterial faeco-oral Slight to moderate

Soil-transmitted worms Great

Beef & pork tapeworms Great

Water-based worms Moderate

Insect vector Slight to moderate

After Feachem et al. (1983)

Risk factors for infection with Giardia in Salvador, Brazil

Source: Prado et al. (2003) Epidemiol. Infect. 131(2): 899-906

Risk factor Odds Ratio(95% CI)

Nº of children in family < 5 years 2.08(1.32-3.27)

Solid waste not collected 1.97(1.22-3.16)

Presence of visible sewage near house

1.85(1.16-2.96)

Absence of a toilet 2.51(1.33-4.71)

Fly control in Gambia

Period prevalence of diarrhoea (%)Wet season Dry season

Intervention village 14 6Control village 19 8Relative risk 0.78 0.74

Mean reduction in diarrhoea prevalence 24%(Mean reduction in trachoma incidence 75%!)

Source: Emerson PM et al. (1999) Lancet 353: 1401-1403

Individual households

No toilet With toilet

Communities as a whole

No drainage Drains only Drains &sew ers

Intestinal worms in Salvador, Brazil

Noinfrastructure

Drainage only Drains &sewers

Trichuris Ascaris hookworms

Drainage and ascariasis in Salvador, Brazil

___________ ________ Without drains With drains

Prevalence of infection (%) 66.4 47.1

Significance of household clustering NS *

No. of significant household risk factors

Relative risk of reinfection (9 months)(95% Confidence Interval)

Correlation of infection/reinfection egg counts(Pearson's r; N = no. of children infected twice) Significance of correlation _______________________________________________________________________

* p < 0.001

No. of significant household risk factors 5 9

Relative risk of reinfection (9 months)(95% Confidence Interval)

Correlation of infection/reinfection egg counts (Pearson's r; N = no. of children infected twice) Significance of correlation_______________________________________________________________________

* p < 0.001

Relative risk of reinfection (9 months) 1.30 2.35(95% Confidence Interval) (1.12-1.52) (1.93-2.86)

Correlation of infection/reinfection egg counts (Pearson's r; N = no. of children infected twice) Significance of correlation_______________________________________________________________________

* p < 0.001

Relative risk of reinfection (9 months) 1.30 2.35(95% Confidence Interval) (1.12-1.52) (1.93-2.86) Correlation of infection/reinfection egg counts 0.05 0.23(Pearson's r; N = no. of children infected twice) (N=250) (N=166)Significance of correlation NS *_______________________________________________________________________

* p < 0.001

Public domain transmission:

Externalities applyControl requires public action: - investment in infrastructure,or - regulation (by-laws, quality standards)

Public domain transmission:

Externalities applyControl requires public action: - investment in infrastructure,or - regulation (by-laws, quality standards)

Domestic domain transmission:

A question of hygiene behaviourControl requires health promotion - but infrastructure may also be necessary

WardCity

River & Environs

Peri-domestic

(street, school, work-place)

Public and domestic domains

Water Treatment

Peri-domestic

WardCity

River & Environs

(street, school,

work-place)

Raw water intake

Transmission Line, and Storage

Primary Distribution

Network

Secondary Distribution

Network

House Connection

Peri-domestic

(street,school, workplace)

Central Treatment Works

Primary Mains

Street Mains

House Connections

Brown vs. Green agenda

“The problems of the poorare suffered by the poorand dealt with by the poor”

Marianne Kjellen

Brown vs. Green agenda

“The problems of the poorare suffered by the poorand dealt with by the poor;

The problems of the richare suffered by the publicand dealt with by the Government”

Marianne Kjellen

The health impact of sanitation Sandy Cairncross Professor of Environmental Health London School of...

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