Health and Environment: What Policymakers Need to Know

Maureen Cropper

University of Maryland and World Bank Camp Resources, August 2008

Talk is from a Developing Country Perspective

What environmental health questions are asked at the World Bank?

For each of the following areas: Outdoor air pollution Indoor air pollution Water and sanitation

What are the key policy questions? What do we already know? What do we need to know?

What Environmental Health Questions Are Asked at the World Bank?

What is the burden of disease attributable to specific environmental risk factors?

Computations performed in all Country Environmental Assessments (CEA)

What are the health benefits of projects that reduce risk factors?

Community water and sanitation projects Projects to reduce power plant emissions Projects that reduce household dependence on

biomass

What are the least-cost methods of reducing maternal and child mortality? (Achieving Millennium Development Goals 4 and 5)

Outdoor Air Pollution: The Policy Issues What are the health effects of air pollution in highly

polluted developing country cities? What proportion of deaths is attributable to air pollution

compared to “clean” levels? (WHO question) What are the benefits of small reductions in air pollution

from existing levels, as could be achieved by realistic pollution control schemes?

This question is challenging because what we know about the health effects of air pollution comes from cities with pollution levels 1/10 of Delhi and Beijing.

What are the costs and effectiveness of different measures to control air pollution?

AIR POLLUTION IN INDIAN AND CHINESE CITIES: 2002

180

197

166175

27 31

11 10

67

152

7 40

50

100

150

200

Delhi Kanpur Beijing Shijiazhuang Washington_DC Birmingham, AL

μg/m3

PM10

SO2

Health Effects of Outdoor Air Pollution

How are health effects measured? Exposure = Ambient concentrations (e.g., μg/m3 of

PM2.5) Concentration-response functions relate ambient pollutant

concentrations to mortality, morbidity Example: Pope et al. (2002) estimate a proportional

hazard model relating mortality (by cause) to PM2.5 for the US

Relative risk of mortality at current level C1 relative to cleaner level C0 is given by

RR = exp(βC1)/exp(βC0) = exp(β∆C) Cases attributable to air pollution, or avoided by reducing

pollution from C1 to C0 are given on the next slide

Computing Health Effects Attributable to Air Pollution

Let fP = incidence at current pollution level (C1)

fc = incidence at clean pollution level (C0)

P = size of exposed population

Cases attributable to ∆C = (fP – fC)*P

fP = fC*RR

Attributable cases = [(RR-1)/RR]*fP*P

What Do We Know from the Epidemiological Literature? - I

From time series studies, we have a good understanding of the impacts of short term exposures to PM and other pollutants on

Mortality Hospital admissions and ER visits Restricted-activity days

Time series studies relate daily deaths (or hospital admissions) to air pollution, weather variables

Effect of air pollution on deaths 2-3 days hence Dozens of such studies, showing consistent results

(see next slide), including studies in LDCs Impacts underestimate the effects of a lifetime of

exposure

Multi-city Study Comparisons of Excess Risk for 10 µg/m3 PM10

Study (#cities) % Change in Total Mortality

PAPA (4) 0.6 (0.3, 0.9)

NMMAPS (20) 0.3 (0.2, 0.4)

Schwartz (10) 0.3 (0.1, 0.6)

NMMAPS (90) 0.2 (0.1, 0.3)

APHEA (29) 0.6 (0.4, 0.8)

Canada (8) 0.8 (0.3, 1.3)

Asian cities (4)*

0.5 (0.2, 0.8)*Bangkok, Inchon, Seoul, Hong Kong

What Do We Know from the Epidemiological Literature? - II

What is less well measured is the impacts of long-term exposures on mortality, chronic illness

Prospective cohort studies that follow a large sample of individuals for 10-20 years are, in principle, capable of measuring these effects

Famous examples include the American Cancer Society study (Pope et al., 1995, 2002); Harvard Six Cities Study (Dockery et al., 1993)

Recent studies in the Netherlands and Switzerland, but none in LDCs

All studies rely on cross-sectional variation in air pollution to measure exposure; Omitted variable bias a concern in spite of rich set of individual-level covariates in some studies

Problems with Current Analyses

Mortality effects from TS, cohort studies differ by an order of magnitude – so it matters which we use

Percentage change in deaths per 10 μg/m3 change in PM10

0.2 – 0.6% in time series studies 3% in Pope et al. (2002)

Problem in extrapolating cohort studies from North America and Western Europe to air pollution levels 10 times higher in LDCs

Form of RR function used in all epi studies is approximately linear, implying that risks associated with PM in Beijing or Delhi are unbelievably large

Attributable fraction of deaths (compared to background levels) in Beijing would be over 30% if used NAWE cohort results

Relative Risk Implied by Pope et al. (2002) at Different PM10 Levels

1

1.1

1.2

1.3

1.4

1.5

1.6

0 50 100 150 200 250

Pope WHO

Outdoor Air Pollution: What Do We Need to Know?

The effects of long-term exposure to air pollution on mortality in developing countries

In the interim, a logarithmic RR function has been estimated using the Pope et al. data. This extrapolates results outside of the range of the study data, but produces AFs that pass the laugh test

Impacts of PM, Ozone on chronic bronchitis, cardiovascular disease and asthma

Interaction between socioeconomic status and effects (Are the poor affected more?)

Species analysis to determine which components of PM are most harmful (to help target control efforts)

Indoor Air Pollution: The Policy Issues What are the health effects of exposure to IAP?

What proportion of respiratory deaths in children < 5 is attributable to IAP? (WHO question)

How does IAP interact with other risk factors in affecting ARI in children? (Also ARI and COPD in women.)

What are the effects of improved stoves and ventilation measures on:

Indoor air pollution levels Health of women and children

How does this depend on human behavior? How can households be encouraged to adopt these

measures?

Health Effects of Indoor Air Pollution

How are health effects measured?

Ideally, measure exposure by indoor concentrations of PM or even personal exposures

Relate exposure to health effects using a concentration-response function (as for outdoor air pollution)

This is rarely done, but many studies documenting indoor PM, CO concentrations and personal exposures

In most studies “exposure” is measured by use of solid fuels for cooking and/or whether individual is near fire or stove

Most studies estimate an odds ratio: odds of the health outcome in the exposed relative to the unexposed group

What Do We Know from the Epidemiological Literature? - I

Most frequently studied outcomes are pneumonia or Acute Lower Respiratory Infection in children < 5

Lung cancer, cataracts in women ALRI, Chronic Obstructive Lung Disease in women Most studies measure morbidity; OR assumed same for

mortality

What types of studies? Recent meta-analysis of IAP and ALRI in children < 5 (Dehrani et al., 2008)

27 ORs from 24 studies 15 from case-control studies; 2 from a randomized trial 7 from cohort studies; 3 from DHS studies

What Do We Know from the Epidemiological Literature? - II

With exception of Guatemala randomized trial (Smith et al. 2007), literature is based on cross-sectional variation in use of solid fuels

Controlling for confounding factors a concern in most studies

Controls in case-control studies may be inappropriate (well-child visits)

No attempt in studies cited to use matching techniques OR from randomized trial = 1.28; = 1.79 based on all

studies; = 1.54-1.65 after controlling for publication bias

For comparison, OR = 2.3 used in WHO’s Comparative Quantification of Health Risks (2004)

Indoor Air Pollution: What Do We Need to Know? - I

We need to better understand the magnitude of health effects:

OR = 1.28 implies that 22% of ALRI attributable to IAP OR = 2.3 implies that 57% of ALRI is attributable to IAP

We need to understand the mortality impacts of IAP; for this we will likely have to rely on large household surveys

We would like to relate health effects to indoor concentrations

Indoor concentrations have been well measured and measures to reduce them have been studied

Indoor Air Pollution: What Do We Need to Know? - II

How to induce behavioral change? Improved stoves exist that reduce fuel

consumption and improve indoor air quality, but their uptake has been slow

Must understand better factors behind stove choice; joint use of clean and dirty fuels

How to communicate health impacts of IAP to households? Nuisance effects are well understood but not longer-term health effects

Water, Sanitation and Hygiene: The Policy Issues

What are the health effects of lack of access to WSH?

What proportion of diarrhea deaths in children < 5 is attributable to lack of WSH? (WHO question)

How does lack of WSH interact with malnutrition, Vitamin A deficiency, lack of oral rehydration therapy?

What are the health effects of: Providing sanitation at the community level Providing water at the community level Piped water connections inside the home Source water treatment Home drinking water treatment

How do these effects depend on (a) human behavior (hand washing, breast feeding), (b) level of other interventions; (c) proportion of the community receiving the intervention?

Health Effects of Lack of Water, Sanitation and Hygiene (WSH)

Focus on effects on diarrhea How are health effects measured?

WSH breaks oral-fecal contamination route by which diarrhea is transmitted; no exposure-response relationship

Evaluate impact of level of provision of WSH on RR of diarhhea (WHO approach, explained on next slide)

Evaluate impact of specific interventions (e.g., home drinking water disinfection) on RR of diarrhea

Most studies examine RR of morbidity, not mortality Concern that case fatality rate could be higher in

households without WSH (implying RR for mortality underestimated)

WHO Measures of Provision of WSH

Level 6: No improved water supply; no basic sanitation

Level 5a: Basic sanitation; no improved water supply Level 5b: Improved water supply; no basic sanitation Level 4: Improved water supply and basic sanitation Level 3: Level 4 + Improved water quality or

hygiene Level 2: 98% of population has improved water

supply and sanitation Level 1: Ideal situation (RR = 1)

WHO Estimates of Reduction in Diarrhea Incidence

From unimproved water and sanitation to: Improved sanitation only 37.5% Improved water only

20.8% Improved water and 37.5%

sanitation

From improved water and sanitation add: Clean drinking water or 35-45%

hygiene

Problems with WHO Analysis

First three numbers on previous slide come from Esrey (1996) based on data from DHS surveys in 12 countries

WHS has no statistically significant effects on diarrhea in rural areas in this article!

In computing fraction of diarrhea attributable to WSH, must consider other factors: malnutrition, vitamin A and zinc deficiencies

To do this correctly requires studies that examine multiple risk factors

In Comparative Quantification of Health Risks, WHO analyzes factors one at a time and attributes 160% of diarrhea to different risk factors!

WSH: What Do We Know? - I

HH drinking water treatment appears highly effective 50% reduction in diarrhea in meta-analysis of 35 RCTs (Clasen

et al. 2007) Results appear independent of level of sanitation

Point-of-use treatment more effective than source treatment (no significant effect from the latter)

But questions remain: Why is there no effect from multiple interventions (hygiene

instruction + point-of-use treatment)? (See Luby et al. 2006) How good is long-term compliance? How to induce greater compliance among the poor?

WSH: What Do We Know? - II

Hand washing also appears effective 50% reduction in diarrhea in meta-analysis of 7

intervention studies (Curtis and Cairncross 2003; Fewtrell et al. 2005)

24% reduction in acute respiratory infections in 8 intervention studies (Rabie and Curtis 2006)

Impact of piped water connections WHO says “no evidence” but: Jacoby and Wang (2004) estimate competing hazards

model using data from China 1992 NFHS; safe water reduces diarrhea morality by 50%; ARI mortality by 40%

Jalan and Ravallion (2003) apply propensity score matching to Indian NFHS; find average treatment effect = 21% reduction in diarrhea; but no effect when mother’s education is ≤ primary school

WSH: What Do We Need to Know?

What are the impacts of community water and sanitation systems on diarrhea and other diseases?

What are the impacts of various interventions on diarrhea mortality?

What are the impacts of various interventions on malnutrition?

What is effective in promoting long-term hygiene behavior modification?

A Closing Note: Is Valuation Important?

Can use cost-effectiveness analysis in evaluating interventions; this is routinely done at the Bank

No official Bank position on health valuation for benefit-cost analyses

Human capital approach always used to value mortality Cost of illness approach to value morbidity VSL, WTP sometimes estimated using benefits transfer

Use of WTP v. COI can affect results by a factor of 4-5 or more

More valuation studies need to be done in developing countries