Cost effectiveness of epidemiological monitoring

The Science of the Total Environment, 32 (1984) 345--351 Elsevier Science Publishers B.V., A m s t e r d a m -- Printed in The Netherlands

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COST EFFECTIVENESSOF EPIDE~IOLOGICAL MONITORING J.S. PLISKIN1 1Department of I n d u s t r i a l Engineering and Management, and University Center for Health Sciences, Ben Gurion University of the Negev, PO Box 653, Beer Sheva 84105, I s r a e l .

ABSTRACT Epidemiological monitoring (EPM) is emerging as a frequent counterpart to environmental monitoring (ENM). EPM and ENM are not a l t e r n a t i v e s to each other but rather complement each other. Each cannot be evaluated on i t s own merit but rather on i t s c o n t r i b u t o r y e ff e c t s in conjunction with the other. The effectiveness of EPM depends p r i m a r i l y on the types of action which i t is designed to t r i g g e r . The benefits may be evaluated in terms of the prevention of adverse health outcomes on the one hand, and from costs saved due to avoidance of unnecessary controls on the other. Nothing d e f i n i t i v e can be said about the cost-effectiveness of EPM in general. Every context and s et t ing require a separate analysis. The attractiveness of introducing EPM, perhaps in conjunction with ENM, is i t s more immediate linkage to action and protective measures. Large scale energy developments seem to arouse the broadest and most a r t i c u l a t e expressions of community concern of a l l new applications of technology.

The p u b l i c ' s eyes focus more and more on decisions a f f e c t i n g technical

aspects, fuel consumption, emissions control and health monitoring.

The f i r s t

three components can be more r e a d i l y evaluated in terms of t h e i r economic impact and hence accepted or not by the community.

However, impact on health, even i f

understood and recognized, is measured by d i f f e r e n t yardsticks and is not e a s i l y commensurate with economic scales. There is an ever increasing demand to protect the public from environmental health hazards.

This demand is f r e q u e n t l y triggered by elevated l e v e l s of

anxiety in the population.

This anxiety is sometimes out of proportion to the

possible consequences and the p r o b a b i l i t i e s of r e a l i z i n g them.

This is

e s p e c i a l l y prevalent where such outcomes as cancer and b i r t h defects are perceived as possible risks.

This is where epidemiological monitoring (EPM)

may play a major r o l e in preventing damage to health, be i t from environmental hazards or from occupational ones.

EPM may also play a fundamental r o l e in

r e l i e v i n g public anxiety. As defined in t h i s issue, EPM is performed f o r the purpose of taking appropriate and t i m e l y action to prevent damage to health.

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A key question to

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answer before EPM is undertaken is whether such a surveillance is at a l l f e a s i b l e , and i f so, do the benefits j u s t i f y costs.

This paper w i l l discuss

some of the issues that bear on the cost-effectiveness of EPM. COSTS OF EPM AND COMPARISONWITH ENM EPM, i f f e a s i b l e , is generally considered less expensive than environmental monitoring (ENM). The underlying reason behind t h i s conjecture is that EPM is usually not a process in which new data sets are developed but rather e x i s t i n g data are used in new ways.

When done properly, EPM is r e l a t i v e l y cheap.

end points of health outcomes are already there.

The

For example, deaths are

recorded; discharge diagnoses are a v a i l a b l e from hospitals; cancer r e g i s t r i e s accumulate a l l new incident cases (and can be linked with demographic and treatment v a r i a b l e s ) ; extensive data on a l l b i r t h s provide valuable information on congenital malformations.

The above data are collected and reported at given

time points regardless o f whether they are to be incorporated in a monitoring system.

The data are already there and may only require a fresh look and new

analyses.

Hence, most surveillance systems are adaptations of e x i s t i n g data

systems rather than new systems.

The adaptation in the margins is r e l a t i v e l y

inexpensive and hence the p o te n t i a l attractiveness of EPM. There are many instances where EPM does require setting up new data bases. An example is provided in t h i s issue by Toeplitz et al (1) f o r a new c o a l - f i r e d power s t a t i o n .

In that example, i n t e r e s t i n g l y , even monitoring with new data

c o l l e c t i o n is several f o l d cheaper than ENM. When EPM is referred to as r e l a t i v e l y inexpensive, the reference point is usually ENM, leading perhaps to believe that EPM is a cheaper substitute f o r ENM. This is d e f i n i t e l y an erroneous i n t e r p r e t a t i o n .

ENM and EPM are not

a l t e r n a t i v e s to each other but rather complement each other.

Each cannot be

evaluated on i t s own merit but rather on i t s value in conjunction with the other.

Therefore, comparing costs is inappropriate by the same token that

cheap bread is not a substitute f o r the more expensive meat but rather complements i t in a balanced d i e t . There are cases where ENM or EPM could be evaluated separately simply because the other a l t e r n a t i v e is not f e a s i b l e . an example where EPM is at a premium.

Legionnaires disease provides

I t was EPM that drove the i n v e s t i g a t o r y

process without any ENM, simply because the only a v a i l a b l e data r e la t e d to disease and not to any underlying agent. Acid rain provides an example of the reverse.

We have reasonably good

understanding of the level of a c i d i t y on lakes and how i t changed over time. We have good ideas about the source ( f o s s i l fuel burning power plants) but there is no known l i n k between a c i d i f i c a t i o n of lakes to health outcomes.

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POTENTIAL BENEFITS OF EPM Once we r e a l i z e that comparison of costs w i l l not be b e n e f i c i a l we must turn to evaluate what benefits w i l l be attained as a r e s u l t of these costs.

This

requires a thorough c o s t - b e n e f i t analysis as with any other public p o l i c y program a f f e c t i n g the population.

Since we are t r y i n g to protect the health o f

the population one component of our b e n e f i t measures w i l l r e l a t e to health outcomes and the analyses would go along the lin e s of commonly used approaches (2). The second component involves avoidance o f i n s t a l l i n g unnecessary controls. As EPM involves the periodic measurement and evaluation of health status, and i f health protection o f the population is the objective of both ENM and EPM, then EPM is considered to have greater v a l i d i t y .

Again, t h i s does not mean in

i t s e l f that EPM is more c o s t - e f f e c t i v e than ENM. Any c o s t - b e n e f i t or cost-effectiveness of monitoring programs a f f e c t i n g health must evaluate the "costs" of f a l s e l y p o s i t i v e or f a l s e l y negative outcomes of monitoring.

A false negative i n t e r p r e t a t i o n may be a more costly error

in terms of health outcomes and is commonly viewed as the more serious e r r o r in EPM.

A false p o s i t i v e conclusion w i l l usually lead to unnecessary technological

controls and other unnecessary p r o t e c t i v e actions whose outcomes can usually be measured on economic scales.

However, f o r any policy decision, we cannot

r e f r a i n from evaluating costs versus benefits even i f measured on d i f f e r e n t scales.

Such an evaluation requires making e x p l i c i t tradeoffs between monetary

costs and health benefits and before t h i s is done one cannot say which false i n t e r p r e t a t i o n is the more serious one.

The economic costs of a f als e i n t e r -

p r e t a t i o n ( e . g . , unnecessary controls) may, in f a c t , outweigh the health implications of a f a l s e l y negative conclusion. I t is very d i f f i c u l t general terms.

to put cost-effectiveness considerations of EPM in

Every problem and context warrant a separate evaluation.

Cancer and b i r t h defects predominate among the causes of anxiety associated with environmental hazards and are frequently the major d r i v i n g force in the i n i t i a t i o n of EPM. However, cancer detection and prevention w i t h i n the scope of EPM is rather i n e f f e c t i v e because of i t s long latency. CANCER AS A MODEL I t may take as many as 20 years f o r a cancer to be detected a f t e r exposure to an environmental carcinogen.

EPM may reveal the cancer but how does one go back

and l i n k the cancer to a s p e c i f i c agent or p o l l u t a n t ?

I f the detected cancer is

lung cancer, how do we know how much of i t is due to smoking and how much is linked to environmental agents? Cancer is most problematic with EPM but since i t is perhaps the most instrumental in i n i t i a t i n g i t we must address i t separately. EPM would be most e f f e c t i v e in s i t u a t i o n s where there is a promptly i d e n t i f i e d marker f o r a condition.

In t h i s respect, monitoring occupational health

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may serve as an e x c e l l e n t paradigm f o r EPM.

In the workplace, levels of

exposure are high, concentrations of carcinogenic agents are high, there is a c l e a re r a b i l i t y to define duration of exposure, short-term physiological or p r o t o t o x i c effects can be sought, and the t a r g e t population is f ix ed and well defined.

During the last 20 years, examples of occupational carcinogenesis have

been increasingly recognized because of extremely high risk r a t i o s (often a function of the r a r i t y of the disease in the general population) and a very high incidence rate among occupationally exposed persons.

Sources of occupational

risk are more obvious than sources of other environmental problems, which have a more complex set of emission-exposure l i n k s . Lung cancer demonstrates the d i f f i c u l t i e s

of EPM f or environmental hazards.

On the other hand, mesothelioma which is a cancer of the l i n i n g of the chest or abdominal cavity is unique to asbestos exposure (3) and angiosarcoma of the l i v e r is uniquely associated with exposure to PVC ( p o l y - v i n y l - c h l o r i d e ) ,

The

cancers that EPM in the workplace can pick up are those that have a very low incidence in the general population but have a very high incidence in the workplace. One can agree that even i f a s p e c i f i c agent in the workplace or environment is targeted as a possible carcinogen, i t may take years of EPM to uncover the l i n k to health status.

On the other hand, ENM would not lead to any conclusions,

not to speak of actions.

The r e l a t i v e attractiveness o f EPM in any context,

reemerges in i ts l i n k to p r o t e c t i v e actions.

I t may be worthwhile to wait these

20 years f o r previously u n i d e n t i f i e d r i s k s : t o reap the benefits o f avoiding future exposure.

For i d e n t i f i e d risks, an a l t e r n a t i v e , e a r l i e r reacting

mechanism must be sought. Even in cases with long latency, EPM leads to more informed decisions than ENM because the l a t t e r does not o f f e r knowledge about the health effects of e x i s t i n g or changing levels o f an agent or p o l l u t a n t .

EPM, on the other hand,

i d e n t i f i e s changes in health and can result in f a s t e r action, i f only to c o l l e c t new confirmatory data. However, with cancers and other diseases we may find that EPM is not s e n s i t i v e enough to some health changes and may, t h e r e f o r e , be o f l i t t l e benefit.

EPM f o r cancer could have added benefits i f the target is switched

from detecting cancers to monitoring f o r other unfavorable health effects from known or possible carcinogenic exposures (4).

These adverse health effects may

serve as e a r l y warning signals and carry the potential of leading to various protective actions.

Thus a public outcry due to possible carcinogenesis may

lead to EPM which in turn may a l l e v i a t e the anxiety even though i t s target is not cancer detection d i r e c t l y .

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Let us return to screening f o r cancer and reexamine occupational health as a paradigm f o r EPM.

In the general population, emphasis in cancer screening

is on e a r l i e r disease detection; while in i n d u s t r i a l populations more benefits seem possible by i d e n t i f y i n g p o t e n t i a l carcinogens and l i m i t i n g worker exposure (5).

I f t h i s is indeed the picture in the workplace, then perhaps

one may t r y to project to environmental hazards and conclude that when cancer is the health a t t r i b u t e considered, then ENM may carry more p o t e n t ia l b e n e f i t than EPM. Again, the question is at what cost? There has been almost no work on the development of c o s t - e f f e c t i v e strategies to screen substances f o r carcinogenicity, due p r i m a r i l y to lack o f data on c h a r a c t e r i s t i c s o f the screening tests. A number

of chemicals or i n d u s t r i a l processes associated with excess

cancer risk have been discovered (6).

There are, then, large amounts of data

concerning e t i o l o g i c factors in occupational cancer that are more f i r m l y established than risk f a c t o r data a v a i l a b l e f or most general population based cancers.

Thus, the emphasis o f current data bases and current research thrust

is the examination of h i g h - r i s k i n d u s t r i a l groups by epidemiological studies and surveillance (7-9).

On the other hand, there are f a r less data a v a i l a b l e

to develop natural h i s t o r y models f o r occupational cancers.

This is equally

true f o r the unique cancers such as angiosarcoma of the l i v e r or mesothelioma, where the number of i n d i v i d u a l s with these p a r t i c u l a r diseases has been small to date.

(However, the 11 m i l l i o n persons who have had occupational exposure

to asbestos w i l l , future.)

unfortunately, provide an extensive data base f o r the

Rather, the data that are a v a i l a b l e r e l a t e to carcinogenic p o t e n t i a l

of certain substances and hence the motivation to screen f o r substances rather than disease. For any screening program in occupational environments to be undertaken, certain conditions must p r e v a i l .

That i s , there is a disease that progresses

and as the duration of the p r e c l i n i c a l phase increases, prognosis d e t e r i o r a t e s ; there is a screening technique that can detect disease e a r l i e r in i t s course; and e a r l i e r detection improves s u r v i v a b i l i t y .

Without some evidence of the

v a l i d i t y of these premises, the high risk o f i n d u s t r i a l or environmentally exposed populations in and of i t s e l f provides l i t t l e

basis f o r i n s t i t u t i n g

health monitoring programs. There have been no proven benefits in terms o f increased survival in any of the occupational cancer screening programs to date, although disease can be detected e a r l i e r (10,111. Those cancers f o r which there is more evidence o f the value o f screening ( i . e . breast, cervical and c o l o r e c t a l ) are not cancers that have been unequivocally linked to any p a r t i c u l a r i n d u s t r i a l groups or environmental exposure.

For environmental hazards the s i t u a t i o n is even more

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complicated in l i g h t of the heterogeneity of the population and the many e x i s t i n g confounding variables ( e . g . , smoking in the case o f lung cancer). The importance of chemical carcinogenesis in i n d u s t r i a l populations and the large body of l i t e r a t u r e devoted to the i d e n t i f i c a t i o n and d e f i n i t i o n of chemical carcinogenesis raises the p o s s i b i l i t y of a d i f f e r e n t approach to cancer screening programs - screening substances rather than people.

Projected

to environmental hazards, t h i s c a l l s f o r an enhanced role f or ENM. A problematic issue both f o r occupational and environmental carcinogenesis are the long l a t e n t periods of up to twenty years between the time o f exposure to a substance or p o l l u t a n t and the c l i n i c a l surfacing of a tumor.

Hence, i f

reliance is placed on human EPM of the cancer endpoint there w i l l have been a great deal o f exposure to substances before t h e i r carcinogenic potential is determined.

Hence the value of screening f o r cancer i t s e l f may be questionable

in general. EPM may be valuable in decisions a f f e c t i n g a l l o c a t i o n of occupational health resources.

This can be achieved as a by product of studies to determine the

cost-effectiveness of various monitoring programs.

One must s t i l l

remember

that even the most c o s t - e f f e c t i v e program among several programs may not j u s t i f y i t s costs. OTHER CONSIDERATIONS An important aspect of EPM which cannot be ignored in a cost-effectiveness or a f e a s i b i l i t y analysis is the determination of baseline levels of exposed populations.

As demonstrated elsewhere in this journal (1) a study of baseline

levels before a power plant became operational avoided the risk o f an erroneous false p o s i t i v e i n t e r p r e t a t i o n o f health effects of t h i s plant.

Such a false

p o s i t i v e i n t e r p r e t a t i o n could have led to i n s t a l l a t i o n of SO2 scrubbers, the cost of which could have reached $100,000,000 over the l i f e span of the plant. These costs are several times greater than costs of ENM and EPM combined! Thus, any f e a s i b i l i t y and c o s t - b e n e f i t analysis of EPM should include examination of baseline studies. The above study (1) also presents another side to EPM which g r e a t ly enhances i t s value.

This relates to the time frames or horizon at which EPM is designed.

The described program permits detection of short-term effects based on increases in health service requests, medium-term effects by repeat examination of selected panelists, and long-term effects based on monitoring pulmonary conditions among school children. As we have seen above, nothing d e f i n i t i v e can be said about the general cost-effectiveness of EPM. Any analysis must r e l a t e in a specific environment.

to a s p e c i f i c population

I t is quite obvious, though, that the c a p a b i l i t y of

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l i n k i n g EPM to ENM adds b e n e f i t measures to both.

I t is generally true that

the value of ENM increases when there is a continuous EPM. EPM may be used as a confirmatory procedure f o r ENM or vice versa.

The effectiveness of EPM

depends p r i m a r i l y on the types of action which i t is designed to t r i g g e r .

ACKNOWLEDGEMENTS I would l i k e to thank Professor John Goldsmith and Dr. David Gute f o r t h e i r valuable i n s i g h t and guidance.

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4. 5. 6.

7.

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