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
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.
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(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)
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.
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.
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.
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
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.
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
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.
.
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.
‘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
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No toilet With toilet
Dia
rrh
oea
inci
den
ce
Communities as a whole
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No drainage Drains only Drains &sew ers
Dia
rrh
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den
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Intestinal worms in Salvador, Brazil
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Noinfrastructure
Drainage only Drains &sewers
Pre
vale
nce
(%
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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
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
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
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
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
Home
WardCity
River & Environs
Peri-domestic
(street, school, work-place)
Public and domestic domains
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
Peri-domestic
Ward
City
(street,school, workplace)
Home
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