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
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Health may be a major benefit, but it is not the main one in the eyes of the consumer.
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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
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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
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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.
0
10
20
30
40
50
60
70
(a) Sanitation (b) Wateravailability
(c) Waterquality
(d) Hygienepromotion
(e) Handwashing
Red
uct
ion
in
dia
rrh
ea m
orb
idit
y (%
)
Previous reviews Fewtrell et al. (2004)
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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
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Health impact
measurement; a
cautionary tale
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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.
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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
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)
Source: Prag JB et al. (1983) Water Master Plan for Iringa, Ruvuma and Mbeya Regions, Tanzania Vol. 13 Ch. 11.
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Health impact measurement; a cautionary tale Village Piped water Dug hole
Namabengo 15/216 ( 7%) 5/70 ( 7%)
Mkongo 37/100 (37%) 39/134 (29%)
Children < 5 years with diarrhoea during previous week
Village Piped water Dug hole
Namabengo 4/216 (1.9%) 1/70 (1.4%)
Mkongo 7/100 (7.0%) 12/133 (9.0%)
Children < 5 years with positive Widal (S. typhi H antigen)
Source: Prag JB et al. (1983) Water Master Plan for Iringa, Ruvuma and Mbeya Regions, Tanzania Vol. 13 Ch. 11.
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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
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Health impact measurement; a cautionary tale Village Piped water Dug hole
Namabengo 15/216 ( 7%) 5/70 ( 7%)
Mkongo 37/100 (37%) 39/134 (29%)
Totals 52/316 (16%) 44/204 (22%)
Children < 5 years with diarrhoea during previous week
Village Piped water Dug hole
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%)
Children < 5 years with positive Widal (S. typhi H antigen)
Source: Prag JB et al. (1983) Water Master Plan for Iringa, Ruvuma and Mbeya Regions, Tanzania Vol. 13 Ch. 11.
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Multivariate analysis is not guaranteed to
remove confounding, especially when
RR < 2
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.
The Clofibrate study; 5-year mortality among at-risk men (%)
Group Compliance with treatment
Relative Risk
p
< 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.
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.
The Clofibrate study; 5-year mortality among at-risk men (%)
Group Compliance with treatment
Relative Risk
p
< 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.
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‘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
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Can television
protect you
from diarrhoea?
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“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.
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Conclusion:
Measuring health benefits is tricky; better to measure intermediate variables
-access
-time saving, cost reduction
-hygiene
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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
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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)
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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)
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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
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Individual households
0
1
2
3
4
5
6
7
No toilet With toilet
Dia
rrh
oea
inci
den
ce
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Communities as a whole
0
1
2
3
4
5
6
No drainage Drains only Drains &sew ers
Dia
rrh
oea
inci
den
ce
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Intestinal worms in Salvador, Brazil
0
10
20
30
40
50
60
70
80
90
100
Noinfrastructure
Drainage only Drains &sewers
Pre
vale
nce
(%
)
Trichuris Ascaris hookworms
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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
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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 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
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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 5 9
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
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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 5 9
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
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Public domain transmission:
Externalities applyControl requires public action: - investment in infrastructure,or - regulation (by-laws, quality standards)
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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
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Home
WardCity
River & Environs
Peri-domestic
(street, school, work-place)
Public and domestic domains
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Water Treatment
Plant
Home
Peri-domestic
WardCity
River & Environs
(street, school,
work-place)
Raw water intake
Transmission Line, and Storage
Primary Distribution
Network
Secondary Distribution
Network
House Connection
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Peri-domestic
Ward
City
(street,school, workplace)
Home
Central Treatment Works
Primary Mains
Street Mains
House Connections
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Brown vs. Green agenda
“The problems of the poorare suffered by the poorand dealt with by the poor”
Marianne Kjellen
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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