Internalional Journal o]" Food Microhioh~gy. 15 (191121 2117-213 ,¢) 1902 Elsevier Science Publishers B.V. All rights reserved 0168-16|15/112/$115.1X)
2117
FOOD 11114811
The economic impact of poultry-borne salmonellosis: how much should be spent on prophylaxis? U.
Persson and S. Jendteg
IliE. 77w Swedish in,~tinae l o t lh'alth i'~conmmc.~. I,,nd. Swe~h'n
Foodborne salmoncllosis constitutes a major IIcalth problem ill many countries. Moreover, the costs associated with salmoncllosis could he considerable. ]'here arc thus strong arguments for preventive effi)rts. Ambitious. often gtw~:rnment-spousored, progralllllles aimed at pleventing and controlling salmonellosis in, fi)r instance, pt~ultry production represent one alternative to lower salmonellosis-relatcd illness ;.1110 econonlic cosls. ()n the other hand° such conlprehensivc progranlmes are rather resource-demanding. From the eeononfic point of view the key problem is to find the optimal level for prophylactic measures. The purpose of this study is Io compare two different approaches to preventing poultry-horne salmonellosis among humans. We identify and compare the economic costs of illness due to poultry-borne salmonellosis and the costs of salmonella control in Enghmd and Wales and Sweden, respectively. An alternative option is then introduced: the collcepl of competitive exclusion (('El. Our results show thai the cost of illness constitutes the major part of the total cost in England and Wales, whereas in Sweden, the control cost amounts to q5~ of the total cost, By using the CE concept, the cosl of illness title to poultry-borne sahnonellosis in England and Wales could be reduced by at least GB£ 12.6 millkm. These advantages apply Io individuals, producers, and to society, and we thus eOllclude thai the CE concept is a very c,'sl-effective way of using scarce resources. Key words: Salmonellosis; Poultry; Prophylaxis: ('ompetitive exclusion
Introduction The epidemiological and economic consequences of food poisoning are often of considerable magnitude, in the short run, communicable diseases such as salmonellosis cause widespread illness and associated use of health-care resources. In the long run, these diseases may rcstdt in disability and chronic illness, loss of productive capacity and income, and substantial resources spent on private and public measures to prevent and ctmtrol additional outbreaks. During 1977-1982 salmonclla infections caused 37% of confirmed foodborne diseases in the U.S. ('orrt',ffumdence to: U. Persson, IIIE, The Swedish Institute fi)r Ilealth Economics, Stora S~idergatan 47, S-222 23 Lund, Sweden.
208
(Zottola, 1988). Furthermore, according to a WHO forecast, foodborne diseases will soon become the second largest cause of morbidity in Europe (Kampelmacher, 1987). in order to prevent or minimise outbreaks of communicable diseases, obviously control measures are necessary. However, the design of such measures is not self-evident. Existing preventive measures and control systems in different countries consist of both public and private, compulsory and voluntary, activities, which vary in extent from one country to another. in this report we firstly assess the economic impact of poultry-borne salmonelIosis in England and Wales, countries with an increasing rate of domestically acquired human salmonellosis, and Sweden, a country with only a low rate of domestic cases. Then we estimate the costs of control and prevention of poultryborne salmonella infections in each country, and finally we introduce an alternative solution: prevention by the concept of Competitive Exclusion (CE) (Nurmi and Rantala, 19731.
Material and Methods
Our estimations of the different types of cost are based on a wlriety of sources in England and Wales and Sweden, and all costs are expressed in 19911 prices (pounds sterling, GB£). Cost o f ill, ess According to 1989 data for England and Wales, the number of cases amounted to 26000, of which 911% were domestic cases (Baird-Parker, 1990; HMSO, 19911). However, on average, this means 500 per million inhabitants compared to Sweden's 7110 per million inhabitants. There is thus reason to believe that under-reporting prevails in England and Wales. Considering the fact that England and Wales have almost six times the population of Sweden, an assumption that Enghmd and Wales have the Swedish salmonellosis rate would mean around 3501X) cases instead of the reported 26111111(i.e. a ratio of 1.35 : I for unreported cases). In the estimate of the costs of salmonellosis in England and Wales, we use the 1.35:1 ratio for the domestic cases, which gives a total of 315911 cases. Using a 33% attribution rate for chickens, as reported in the U.K. (Public Health Service Laboratory, 19901, provides a final total of 111425 cases for the analysis. Health-care resource use, production loss and costs have been estimated from recent U.K. studies (Roberts et al., 1989; Sockett and Roberts, 19901. In 19911, 61143 cases of salmoneilosis were reported in Sweden, of which around 811% were 'imported' cases (Andersson, 1991}). Thus, a calculation of the costs of salmonellosis due to domestic sources must be based solely on the 1179 domestic cases. Since the Swedish control system results in a very low infection rate among chickens we have used an attribution rate of 18% (Gerigk, 19901. This gives a total of 212 cases. Health-care utilization, production loss and cosls h:,ve been obtai:~.ed
2(~ through a recent investigation p e r f o r m e d in collaboration with the D e p a r t m e n t of Infectious Diseases, Central Hospital, Kristianstad, Sweden.
Cost of control As regards England and Wales, o u r aim has been to estimate the costs of the pre-1989 control measures, i.e. before the extension of the control p r o g r a m m e in recent years. According to representatives of the Ministry of Agriculture, Fisheries and Food, the National Farmers" Union, the British feed producers, and the Central Public Health Laboratory, there are no comprehensive estimates of the incremental costs due to salmonella control m e a s u r e s in England and Wales. T h e r e f o r e , our estimate is based on information received partly from authorities and p r o d u c e r s in England and Wales, and partly from our own calculations from Swedish data. T h e Swedish costs of control have been estimated from data supplied by the National Board of Agriculture and representatives of the Swedish chicken produccrs.
Prophylaxis through competitit'e ~:rch~sion Efficacy data for the concept of competitive exclusion (CE) have b e e n o b t a i n e d from four recent studies ( C a m e r o n and Carter, 1991; Schneitz et ai., 1991; Snoeyenbos et ai., 1985; W i e r u p et al., 1988). T h e s e studies all report efficacy rates on birds, and the average reduction in the salmonella contamination rate is 80% c o m p a r e d to controls.
Results
T a b l e ! shows the economic cost of poultry-borne salmonellosis in England and Wales and Sweden. From the table it can be seen that the major part of the cost in
TABLE ! Total economic cost of poultry-borne salmonellosis in England & Wales, and Sweden 1990 prices, GB£x 10 3 Type of cost Direct costs of illness in-patient services outpatient services laboratory tests - drugs Indirect costs uf iiiu~.s,~ - premature mortality - short-terra illness - care of sick children time costs -
-
Total cost
England & Wales 1642 2~)9
1512 163 9215
Sweden 63 16 27 -
2277 293 177
78 5 6
15578
195
2!0 TABLE 11 The annual incremental cost of salmonella control in poultry in England & Wales and Sweden 19911prices, GB£ x 1 0 3 Type of cost
England & Wales
Government costs Producers" costs investments in buildings breeding and parent stock feed broiler breeding slaughter
Sweden 464
-
51111 418
-
-
361111 6655 18111)
-
-
-
-
Total cost
121155
1218
1645 3119 4554
England and Wales is attributed to loss of production due to premature mortality. in Sweden, however, no deaths due to poultry-borne saimonellosis are expected; instead it is sick leave due to short-term morbidity that forms the largest part of the Swedish cost of illness. Table !I illustrates the total incremental cost per year due to control measures against salmonella infections among poultry. T h e comprehensiveness of the Swedish system means a relatively high cost per chicken produced. Using the 1990 production figures of 600 million chickens in England and Wales and 42 million chickens in Sweden means a cost of 10.8 pence per chicken in Sweden, which is more than five times the cost per bird in England and Wales (2.0 pence). Table ili summarises the total expected cost per bird produced in England and Wales and Sweden. However, by using the concept o f C E the rate of salmonellacontaminated chickens, and hence the cost of illness, could be considerably reduced. Assuming an initial 48% contamination rate among chickens in England and Wales (Roberts, 19911, an 80% efficacy rate for C E will reduce the contamination rate to 10%. Assuming that the cost of illness is proportional to the rate of contaminated birds, the cost of illness in England and Wales will thus decrease to 0.5 pence per bird. If the cost of control in England and Wales remains unchanged, then the use of C E means that a drastic reduction of poultry-borne salmonellosis and associated
TABLE 111 Total expected cost per chicken produced in England & Wales and in Sweden 1990 prices, GB pence Type of cost Cost of illness Cost of control
England & Wales 2.6 2.11
Sweden 11.5 11).8
Tolal cost
4.6
11.3
211 T A B L E IV The value of competitive exclusion (('E) in England & Wales. without increasing total salmonellosis cos| 1991) prices. GB pence per bird Lost production due to premature mortality
Value of reducing the risk o f death
Cost of illness Cost of control
t).5 2.0 ( + 2. i CE)
1.2 2.1) ( + 4.9 CE)
Total cost
4.6
8. I
costs could be achieved without increasing the total cost. The difference between the initial and the new total cost - GB£12.6 million or 2.1 pence per bird - could thus be attributed to CE (Table IV). So far we have only considered the production loss as an economic measure of mortality. If, however, we include a value for health per se, i.e. a value for reducing the risk of health loss or death, similar to the one used by the Department of Transport in Great Britain (Jones-Lee, 1990), the benefits of prophylaxis become even more obvious. An additional 'value of life' of GB£0.5 million (Jones-Lee, 1990) increases the initial total cost in England and Wales to GB£49.2 million or 8.1 pence per bird. Applying the CE concept will reduce the contamination rate among chickens as well as illness and related costs among humans to GB£19.9 million or 3.3 pence per bird. If the initial costs of control remain the same, then the difference between the initial and the new total cost - GB£29.3 million or 4.9 pence per bird - could be attributed to CE (Table IV).
Discussion and conclusions The recent British experience provides a typical illustration of the impact of foodborne diseases, in 1988-1989, the so-called salmonella-in-eggs crisis caused a food scare among British people which made egg consumption fall by up to 90% initially. Eventually it cost the Government and the egg producers approximately GB£70 millioo due to increased surveillance and regulatory measures, sales losses and slaughter of more than one million birds (North and Gorman, 1990). During the period March 1989 to December 1990 a total of 1700000 infected birds were slaughtered (Public Health Services Laboratory, i991). There are thus considerable reasons for preventive efforts as regards the spread of salmonella infection. In Sweden, poultry-borne salmonellosis has been reduced to a low level through a comprehensive programme which includes governmental control as well as producers' measures. The cost of this programme is, however,
212 considerable; our estimate shows that it is more than five times as costly as the British system before 1988-1989. However, there are less costly alternatives to the Swedish system. One option is to maintain a level of control such as, for instance, the previous British system which included certain sampling, cleaning and disinfection measures, and combine this with prophylaxis, i.e. the CE concept. This approach would imply a major reduction of salmonella infection among poultry and an associated decrease in the costs of poultry-borne salmonellosis among humans. As the cost of illness forms the main part of the total cost of salmonellosis in England and Wales, and since it is often difficult to get an accurate estimate of costs due to morbidity and premature mortality, we have compared our results with those from a number of U.K. studies from the 1980s (Roberts et al., 1989; Sockett and Roberts, 1990; Yule et al., 1988). The most recent study, Sockett and Roberts (1990), presents a cost per case of GB£789, but this does not include mortality costs. However, the authors estimate that including such costs would increase the cost per case to GB£1200-1500, which could be compared with our estimate of GB£1494 that includes mortality costs. As can be seen from Table IV, the importance of preventive efforts increases as the estimate for the cost of illness is extended to include a value for reducing the risk of death. Thus, from chicken consumers', tax-payers', and from patients' points of view, the issue of preventing poultry-borne salmonellosis could be clearly justified. From the producers' point of view there is a similar reason to adopt prophylactic measures. For instance, in Great Britain, large supermarkets have expressed the necessity to supply salmonella-free chickens to their customers, in practice, it is unlikely that salmonella infections in birds can be completely eradicated, and, therefore, reduction to a 3% contamination rate has been considered a reasonable goal. If we apply this to our previous assumptions it would mean a reduction from 48% to 3% contaminated chickens, i.e. by 94%. Efficacy rates of 96-97% have been reported for the CE concept (Cameron and Carter, 1991; Snoeyenbos et al., 1985), and it thus seems reasonable to assume a 94% efficacy rate for CE. This would reduce the cost of illness even further, and if the cost of control remains unchanged, the new results imply an increase in the value of CE; from 2.1 pence to 2.4 pence per bird, or from 4.9 pence to 5.7 pence per bird if the value for risk reduction is included. Furthermore, the CE concept means a lower level of salmonella infection in contaminated chickens (Nurmi et al., 1991), which reduces cross-contamination among birds. In conclusion, prevention of poultry-borne saimonellosis by using the CE concept is definitely worthwhile both from individuals', producers' and society's point of view. Our results, although they must be considered as conservative estimates, underline the fact that CE is a very cost-effective way of using scarce resources, and that the CE concept combined with a certain level of control and surveillance could be an alternative to more ambitious control and prevention programmes of the Swedish type.
213
References Andersson, Y. ( 199111Zoonotisk salmonella. Epid-aktuellt 13(12), 4-5. Baird-Parker, A.C. (19911) F(r)dborne salmonellosis. Lancet 336. 1231 - 1235. Cameron. D.M. and Carter, J.N. (1991) BROILACT '~. Evaluation of efficacy in prevention of infection with a non-host specific strain of salmonella in broiler chickens, Paper presented at The Symposium on Colonization Control of ltuman Pathogens in Poultry, D~,rwerth. the Netherlands, 17 May 1991. G~'ri~k, K ~Fd ) (IO0m W t | O surveillance programme for control of foodborne infections and intoxications in Europe, Fourth Report, Institute of Veterinary Medicine, Berlin. Her Majesty's Stationery Office (1990) The Microb.ological Safety of Ftmd, Part I, lter Majesty's Stationery Office, London. Jones-Lee, M.W. (1990) The value of transport safety. OxG)rd Rcv. of Econ. Policy 6(2), 39-60. Kampelmachcr, E.M. (1987) Poultry disease and public health. Br. Poultry Sci. 28d), 3-13. North. R. and Gorman. T. ( 199111Chickengate: An independent analysis of the salmonella in eggs ~arc. The lEA Health and Welfare Unit. London. Nurmi, E. and Rantala, M. (1973) New aspects of salmonella infection in broiler pr(~luction. Nature 241,210. Nurmi, E., et al. (1991) Salmonella in poultry, Lancet 337, 61. Public Health Laboratory Service (1990, 19911 Update on salmonella infection. PHLS-SVS, London. Roberts, D. (1991) Salmonella in chilled and frozen chicken, Lancet 337, 984-985. Roberts, J.A.. et al. (1989) Economic impact of a nationwide outbreak of salmonellosis: cost-benefit of early intervention. Br. Med. J. 298, 1227-123(I. Schneitz, C., el al. (1991) Pilot-scale testing of the (bmpetitive Exclusion method in chickens. Br. Poultry Sci. 32, 881-884. Snoeyenbos. G.H. (Ed.)(1985) Large-scale trials to study competitive exclusion of salmonella in chickens. Avian Dis. 29(4), IIX14-101 I. Sockett, P.N. and Roberts, J.R. ( I t ~ ) T h e social and economic impact of salmonellosis. Public Health Laboratory Service, London. Wierup. M., et al. (19881 Epidemiological evaluation of the salmouella-controlling effect of a nationwide use of a competitive exclusion culture in poultry. Poultry Sci. 67, 1026-1033. Yule, B., et al. (19881 Costing of a hospital-based outbreak of poultry-borne salmonellosis. EpidemioL Infect. 100, 35-42. Zottola, E. (I988) Salmonella leads parade as cau,,,e of foodborne illness. Process. Poultry (Nov.-Dec.), 32-34.
2117
FOOD 11114811
The economic impact of poultry-borne salmonellosis: how much should be spent on prophylaxis? U.
Persson and S. Jendteg
IliE. 77w Swedish in,~tinae l o t lh'alth i'~conmmc.~. I,,nd. Swe~h'n
Foodborne salmoncllosis constitutes a major IIcalth problem ill many countries. Moreover, the costs associated with salmoncllosis could he considerable. ]'here arc thus strong arguments for preventive effi)rts. Ambitious. often gtw~:rnment-spousored, progralllllles aimed at pleventing and controlling salmonellosis in, fi)r instance, pt~ultry production represent one alternative to lower salmonellosis-relatcd illness ;.1110 econonlic cosls. ()n the other hand° such conlprehensivc progranlmes are rather resource-demanding. From the eeononfic point of view the key problem is to find the optimal level for prophylactic measures. The purpose of this study is Io compare two different approaches to preventing poultry-horne salmonellosis among humans. We identify and compare the economic costs of illness due to poultry-borne salmonellosis and the costs of salmonella control in Enghmd and Wales and Sweden, respectively. An alternative option is then introduced: the collcepl of competitive exclusion (('El. Our results show thai the cost of illness constitutes the major part of the total cost in England and Wales, whereas in Sweden, the control cost amounts to q5~ of the total cost, By using the CE concept, the cosl of illness title to poultry-borne sahnonellosis in England and Wales could be reduced by at least GB£ 12.6 millkm. These advantages apply Io individuals, producers, and to society, and we thus eOllclude thai the CE concept is a very c,'sl-effective way of using scarce resources. Key words: Salmonellosis; Poultry; Prophylaxis: ('ompetitive exclusion
Introduction The epidemiological and economic consequences of food poisoning are often of considerable magnitude, in the short run, communicable diseases such as salmonellosis cause widespread illness and associated use of health-care resources. In the long run, these diseases may rcstdt in disability and chronic illness, loss of productive capacity and income, and substantial resources spent on private and public measures to prevent and ctmtrol additional outbreaks. During 1977-1982 salmonclla infections caused 37% of confirmed foodborne diseases in the U.S. ('orrt',ffumdence to: U. Persson, IIIE, The Swedish Institute fi)r Ilealth Economics, Stora S~idergatan 47, S-222 23 Lund, Sweden.
208
(Zottola, 1988). Furthermore, according to a WHO forecast, foodborne diseases will soon become the second largest cause of morbidity in Europe (Kampelmacher, 1987). in order to prevent or minimise outbreaks of communicable diseases, obviously control measures are necessary. However, the design of such measures is not self-evident. Existing preventive measures and control systems in different countries consist of both public and private, compulsory and voluntary, activities, which vary in extent from one country to another. in this report we firstly assess the economic impact of poultry-borne salmonelIosis in England and Wales, countries with an increasing rate of domestically acquired human salmonellosis, and Sweden, a country with only a low rate of domestic cases. Then we estimate the costs of control and prevention of poultryborne salmonella infections in each country, and finally we introduce an alternative solution: prevention by the concept of Competitive Exclusion (CE) (Nurmi and Rantala, 19731.
Material and Methods
Our estimations of the different types of cost are based on a wlriety of sources in England and Wales and Sweden, and all costs are expressed in 19911 prices (pounds sterling, GB£). Cost o f ill, ess According to 1989 data for England and Wales, the number of cases amounted to 26000, of which 911% were domestic cases (Baird-Parker, 1990; HMSO, 19911). However, on average, this means 500 per million inhabitants compared to Sweden's 7110 per million inhabitants. There is thus reason to believe that under-reporting prevails in England and Wales. Considering the fact that England and Wales have almost six times the population of Sweden, an assumption that Enghmd and Wales have the Swedish salmonellosis rate would mean around 3501X) cases instead of the reported 26111111(i.e. a ratio of 1.35 : I for unreported cases). In the estimate of the costs of salmonellosis in England and Wales, we use the 1.35:1 ratio for the domestic cases, which gives a total of 315911 cases. Using a 33% attribution rate for chickens, as reported in the U.K. (Public Health Service Laboratory, 19901, provides a final total of 111425 cases for the analysis. Health-care resource use, production loss and costs have been estimated from recent U.K. studies (Roberts et al., 1989; Sockett and Roberts, 19901. In 19911, 61143 cases of salmoneilosis were reported in Sweden, of which around 811% were 'imported' cases (Andersson, 1991}). Thus, a calculation of the costs of salmonellosis due to domestic sources must be based solely on the 1179 domestic cases. Since the Swedish control system results in a very low infection rate among chickens we have used an attribution rate of 18% (Gerigk, 19901. This gives a total of 212 cases. Health-care utilization, production loss and cosls h:,ve been obtai:~.ed
2(~ through a recent investigation p e r f o r m e d in collaboration with the D e p a r t m e n t of Infectious Diseases, Central Hospital, Kristianstad, Sweden.
Cost of control As regards England and Wales, o u r aim has been to estimate the costs of the pre-1989 control measures, i.e. before the extension of the control p r o g r a m m e in recent years. According to representatives of the Ministry of Agriculture, Fisheries and Food, the National Farmers" Union, the British feed producers, and the Central Public Health Laboratory, there are no comprehensive estimates of the incremental costs due to salmonella control m e a s u r e s in England and Wales. T h e r e f o r e , our estimate is based on information received partly from authorities and p r o d u c e r s in England and Wales, and partly from our own calculations from Swedish data. T h e Swedish costs of control have been estimated from data supplied by the National Board of Agriculture and representatives of the Swedish chicken produccrs.
Prophylaxis through competitit'e ~:rch~sion Efficacy data for the concept of competitive exclusion (CE) have b e e n o b t a i n e d from four recent studies ( C a m e r o n and Carter, 1991; Schneitz et ai., 1991; Snoeyenbos et ai., 1985; W i e r u p et al., 1988). T h e s e studies all report efficacy rates on birds, and the average reduction in the salmonella contamination rate is 80% c o m p a r e d to controls.
Results
T a b l e ! shows the economic cost of poultry-borne salmonellosis in England and Wales and Sweden. From the table it can be seen that the major part of the cost in
TABLE ! Total economic cost of poultry-borne salmonellosis in England & Wales, and Sweden 1990 prices, GB£x 10 3 Type of cost Direct costs of illness in-patient services outpatient services laboratory tests - drugs Indirect costs uf iiiu~.s,~ - premature mortality - short-terra illness - care of sick children time costs -
-
Total cost
England & Wales 1642 2~)9
1512 163 9215
Sweden 63 16 27 -
2277 293 177
78 5 6
15578
195
2!0 TABLE 11 The annual incremental cost of salmonella control in poultry in England & Wales and Sweden 19911prices, GB£ x 1 0 3 Type of cost
England & Wales
Government costs Producers" costs investments in buildings breeding and parent stock feed broiler breeding slaughter
Sweden 464
-
51111 418
-
-
361111 6655 18111)
-
-
-
-
Total cost
121155
1218
1645 3119 4554
England and Wales is attributed to loss of production due to premature mortality. in Sweden, however, no deaths due to poultry-borne saimonellosis are expected; instead it is sick leave due to short-term morbidity that forms the largest part of the Swedish cost of illness. Table !I illustrates the total incremental cost per year due to control measures against salmonella infections among poultry. T h e comprehensiveness of the Swedish system means a relatively high cost per chicken produced. Using the 1990 production figures of 600 million chickens in England and Wales and 42 million chickens in Sweden means a cost of 10.8 pence per chicken in Sweden, which is more than five times the cost per bird in England and Wales (2.0 pence). Table ili summarises the total expected cost per bird produced in England and Wales and Sweden. However, by using the concept o f C E the rate of salmonellacontaminated chickens, and hence the cost of illness, could be considerably reduced. Assuming an initial 48% contamination rate among chickens in England and Wales (Roberts, 19911, an 80% efficacy rate for C E will reduce the contamination rate to 10%. Assuming that the cost of illness is proportional to the rate of contaminated birds, the cost of illness in England and Wales will thus decrease to 0.5 pence per bird. If the cost of control in England and Wales remains unchanged, then the use of C E means that a drastic reduction of poultry-borne salmonellosis and associated
TABLE 111 Total expected cost per chicken produced in England & Wales and in Sweden 1990 prices, GB pence Type of cost Cost of illness Cost of control
England & Wales 2.6 2.11
Sweden 11.5 11).8
Tolal cost
4.6
11.3
211 T A B L E IV The value of competitive exclusion (('E) in England & Wales. without increasing total salmonellosis cos| 1991) prices. GB pence per bird Lost production due to premature mortality
Value of reducing the risk o f death
Cost of illness Cost of control
t).5 2.0 ( + 2. i CE)
1.2 2.1) ( + 4.9 CE)
Total cost
4.6
8. I
costs could be achieved without increasing the total cost. The difference between the initial and the new total cost - GB£12.6 million or 2.1 pence per bird - could thus be attributed to CE (Table IV). So far we have only considered the production loss as an economic measure of mortality. If, however, we include a value for health per se, i.e. a value for reducing the risk of health loss or death, similar to the one used by the Department of Transport in Great Britain (Jones-Lee, 1990), the benefits of prophylaxis become even more obvious. An additional 'value of life' of GB£0.5 million (Jones-Lee, 1990) increases the initial total cost in England and Wales to GB£49.2 million or 8.1 pence per bird. Applying the CE concept will reduce the contamination rate among chickens as well as illness and related costs among humans to GB£19.9 million or 3.3 pence per bird. If the initial costs of control remain the same, then the difference between the initial and the new total cost - GB£29.3 million or 4.9 pence per bird - could be attributed to CE (Table IV).
Discussion and conclusions The recent British experience provides a typical illustration of the impact of foodborne diseases, in 1988-1989, the so-called salmonella-in-eggs crisis caused a food scare among British people which made egg consumption fall by up to 90% initially. Eventually it cost the Government and the egg producers approximately GB£70 millioo due to increased surveillance and regulatory measures, sales losses and slaughter of more than one million birds (North and Gorman, 1990). During the period March 1989 to December 1990 a total of 1700000 infected birds were slaughtered (Public Health Services Laboratory, i991). There are thus considerable reasons for preventive efforts as regards the spread of salmonella infection. In Sweden, poultry-borne salmonellosis has been reduced to a low level through a comprehensive programme which includes governmental control as well as producers' measures. The cost of this programme is, however,
212 considerable; our estimate shows that it is more than five times as costly as the British system before 1988-1989. However, there are less costly alternatives to the Swedish system. One option is to maintain a level of control such as, for instance, the previous British system which included certain sampling, cleaning and disinfection measures, and combine this with prophylaxis, i.e. the CE concept. This approach would imply a major reduction of salmonella infection among poultry and an associated decrease in the costs of poultry-borne salmonellosis among humans. As the cost of illness forms the main part of the total cost of salmonellosis in England and Wales, and since it is often difficult to get an accurate estimate of costs due to morbidity and premature mortality, we have compared our results with those from a number of U.K. studies from the 1980s (Roberts et al., 1989; Sockett and Roberts, 1990; Yule et al., 1988). The most recent study, Sockett and Roberts (1990), presents a cost per case of GB£789, but this does not include mortality costs. However, the authors estimate that including such costs would increase the cost per case to GB£1200-1500, which could be compared with our estimate of GB£1494 that includes mortality costs. As can be seen from Table IV, the importance of preventive efforts increases as the estimate for the cost of illness is extended to include a value for reducing the risk of death. Thus, from chicken consumers', tax-payers', and from patients' points of view, the issue of preventing poultry-borne salmonellosis could be clearly justified. From the producers' point of view there is a similar reason to adopt prophylactic measures. For instance, in Great Britain, large supermarkets have expressed the necessity to supply salmonella-free chickens to their customers, in practice, it is unlikely that salmonella infections in birds can be completely eradicated, and, therefore, reduction to a 3% contamination rate has been considered a reasonable goal. If we apply this to our previous assumptions it would mean a reduction from 48% to 3% contaminated chickens, i.e. by 94%. Efficacy rates of 96-97% have been reported for the CE concept (Cameron and Carter, 1991; Snoeyenbos et al., 1985), and it thus seems reasonable to assume a 94% efficacy rate for CE. This would reduce the cost of illness even further, and if the cost of control remains unchanged, the new results imply an increase in the value of CE; from 2.1 pence to 2.4 pence per bird, or from 4.9 pence to 5.7 pence per bird if the value for risk reduction is included. Furthermore, the CE concept means a lower level of salmonella infection in contaminated chickens (Nurmi et al., 1991), which reduces cross-contamination among birds. In conclusion, prevention of poultry-borne saimonellosis by using the CE concept is definitely worthwhile both from individuals', producers' and society's point of view. Our results, although they must be considered as conservative estimates, underline the fact that CE is a very cost-effective way of using scarce resources, and that the CE concept combined with a certain level of control and surveillance could be an alternative to more ambitious control and prevention programmes of the Swedish type.
213
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