Problems in the investigation of foodborne diseases

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Global estimation of food borne diseases

Yasmine Motarjemia

&

Fritz K. Kiifersteinb

For the purpose of decision-making and establish- ing priorities, the importance of having information on prevailing health problems cannot be over- emphasized. This is even more important in the case of countries with frail economies and only limited resources for resolving the most urgent of their health problems.

Foodborne diseases are one of the most widespread health problems in the contemporary world and they have implications both on health and development (1). However, because of the absence of food borne disease surveillance systems in some countries, or weaknesses in existing programmes, reliable information on the magnitude of the problem is not available. It is estimated that the reported incidence of food borne diseases rep- resents less than 10%, or maybe even less than 1%, of the real incidence. Surveys in a few countries indicate that foodborne diseases may be 300- 350 times more frequent than the reported cases tend to indicate (2-4). Furthermore, because of differences in the collection and reporting systems, data from different parts of the world are not usually comparable, thus making a global estimation of foodborne diseases a rather difficult undertaking.

This article describes the constraints in the surveillance of foodborne diseases at national and international levels. Based on a number of assumptions, and following an analysis of the nature of foodborne diseases, their epidemiology, and the possible exposure of populations to the various foodborne pathogens, a semi-quantitative estimation is made of the magnitude of foodborne diseases of microbiological and parasitical origin in various regions of the world.

Constraints In collection of information

Collection of information at international and national levels.

With the exception of cholera (which is subject to the International Health Regulations), there is no obligation to report foodborne diseases interna-

a Scientist, Food Safety and Food Aid Programme, World Health Organization, Geneva, Switzerland.

b Director, Food Safety and Food Aid Programme, World Health Organization, Geneva, Switzerland.

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tionally. Attempts to provide a global picture of foodborne diseases are usually hampered by differences in national surveillance systems, where such systems exist. In most countries, only a few diseases which are or may be of food borne origin appear on the list of notifiable diseases.

In addition, the reported diseases are not pre- sented in a uniform manner, for example, while one country may report the incidence of shigellosis and amoebiasis separately, another may report them jointly under the term dysentery. Again, several foodborne diseases are sometimes reported col- lectively under the term food poisoning. However, the meaning of the term food poisoning varies from country to country, and not infrequently it is used to represent different groups of diseases. Refer- ence to the International Classification of Disease code, which would help to identify the disease in question, is also frequently omitted.

Some countries report the total number of cases of a foodborne disease, including sporadic cases, while others mainly collect information on the number of outbreaks and the number of cases involved in the outbreaks. As a result, information on sporadic cases is not collected in many countries and data from different countries are difficult to compare.

Another constraint- but of a different nature- in collecting information at the international level relates to the repercussions that information on foodborne disease epidemics may have on food trade and tourism. Concern about the possibility of food exports being rejected and/ or loss of tourism have been a disincentive for many governments to release information on foodborne disease epidemics (see the Introduction to this issue).

Weakness of infrastructure.

In most countries the surveillance infrastructure is weak or non-existent. Resources for investigation purposes are meagre: the number of foodborne disease outbreaks may often outstrip the human resources available for investigation. Not infrequently, patients are discouraged from visiting health centres unless their symptoms are serious or persistent. As a result many cases remain unreported.

Furthermore, in many countries, particularly in the developing world, laboratory resources and skills to identify pathogens are scarce, and etiology-

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specific smveillance is often not possible. In the industrialized countries, decreasing resources for the public health infrastructure as well as for medical care have also restricted possibilities for laboratory-based surveillance. In addition, for some agents, e.g. enteric viruses, the absence of a simple and reliable diagnostic test makes surveillance difficult.

Unfortunately, even in countries where such a laboratory-based surveillance is carried out, the data are not regularly communicated to the food control agencies responsible for corrective and preventive actions, such as controlling food opera- tions and/ or providing health education.

Problems in the investigation of foodborne diseases

Investigating food borne disease outbreaks is often difficult, particularly when the source of the out- break is a food which has been prepared in private households, in small food service establishments, or by street food vendors. By the time the investigation begins, there may not be any food left over for analysis. Consequently, evidence is often only cir- cumstantial, and the investigation inconclusive. In such cases, the identification of various risk factors can, over time, provide a statistical basis for assessing the most likely factors in the transmission of foodborne diseases. However, in many cases health authorities are not sufficiently trained or experi- enced to conduct rigorous investigations into foodborne disease outbreaks. The identification of some pathogens (e.g. rotavirus) in foods is also difficult, particularly when these are present in small numbers.

Health authorities' perception of food borne diseases Foodborne diseases have often received low priority in public health programmes because they have been perceived as mild, self-limiting diseases.

Their severe and chronic health consequences have often been overlooked. Sequelae such as can- cer, congenital blindness, reactive arthritis and meningitis resulting from foodborne illnesses do not usually figure in statistics.

In addition, some foodborne diseases such as diarrhoeal diseases - particularly in infants and children - or cholera have traditionally been perceived as waterborne or as being transmitted from person-to-person. The relation between infant diarrhoea (and associated malnutrition) and the contamination of weaning food with pathogens is too often ignored.

Not infrequently, foodborne diseases are mis- diagnosed and mistreated, particularly when the disease is of a new type or one which has been acquired abroad and is unknown to the health workers.

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The general perception that foodborne diseases are benign means that there has been little incentive for investigating, reporting and monitoring the incidence of foodborne diseases beyond their treatment aspects. The economic consequences have also been overlooked.

Lack of information on the real magnitude, health and economic consequences has meant that few resources have been allocated to programmes for the prevention of food borne diseases i.e. food safety (Box 1).

/"lofU.fomotioo ~

Neglect in foodbome Lack of appreciation disease investigation

and surveillance

of health significance of foodbome disease•

'

No priority and resources

/

assigned to food safety

Public perception of food borne diseases

The public's perception of foodborne diseases varies. In some societies diarrhoea is not perceived as a symptom of disease and may even be consid- ered as a normal/ natural occurrence. People may also ignore the role of food and food handling in the transmission of diarrhoeal diseases, and may attribute the diarrhoea to other factors such as indigestion, teething, eating hot (spicy) foods, and superstition. For economic reasons, some population groups may also hesitate to seek medical assis- tance.

In the better-informed societies, people might not seek a physician's help unless the symptoms are severe or long-lasting. Studies in industrialized countries indicate that a relatively small percent- age of people suffering from suspected food borne illnesses consult a health worker: 5% in the Netherlands, 13.5% in New Zealand and 6.2% in Sweden (5,6,2). Although similar data are not available from developing countries, there is reason to believe that an even smaller proportion of cases come to the notice of health services, particularly in so far as the adult population is con- cerned. The motivation to consult a physician not only depends on the severity of the illness but also on the costs involved. Experiences in Zambia indicate that when patients were requested to pay a fee for the medical visit, the number of patients consulting for diarrhoeal diseases, including cholera, decreased.

Rapp. trimest. statist. sanit. mond., 50 (1997)

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\

• • .

I BI

African Region- Region africaine ~ South-East Asia Region - Region de

(AFR) I'Asie du Sud-Est (SEAR)

- Eastern Mediterranean Region - Region de Ia Mediterranee orientale (EMR)

Q

Region of the Americas- Region

0

European Region- Region des Ameriques (AMR) europeenne (EUR)

- Western Pacific Region- Region du Pacifique occidental (WPR)

Global estimation of foodborne diseases

The above-mentioned constraints make it difficult to compare data from different countries and to provide global estimates. Reported incidence data are generally used for the purpose of assessing trends in foodborne diseases in a specific country.

To provide a global picture of foodborne diseases, while offsetting to some extent the uncertainty in the existing data, an attempt has been made to present their estimated occurrence in a semi-quantitative manner. Table 1 presents the re- sult of this work by WHO Regions (see also Map 1).

Here, foodborne diseases are classified into 4 groups, i.e.

(i) not occurring (-)

(ii) occurring occasionally or rarely ( +): the reported annual incidence is in the range of up to 1 case per 100 000

(iii) occurring frequently (++):the reported annual incidence is in the range of 1 to 100 cases per 100 000

(iv) occurring very frequently (+++): the reported annual incidence is over 100 cases per 100 000

The following principles were applied when making the estimates:

• When a disease is considered severe, e.g. botulism, and the degree of under-reporting likely to be low, the available data are taken as an indication of level of occurrence. The source of Wid hlth statist. quart., 50 (1997)

data may either be from the literature or from national epidemiological reports.

• When there is reason to believe that the incidence of a disease is highly under-reported - for instance the disease is mild or self-limiting- the classification is adjusted to correct for the under-reporting. For example, illnesses such as those caused by Staphylococcus aureus and Bacil- lus cereus are likely to be highly under-reported.

Therefore, they are classified one level higher than the available data would suggest.

• Whenever reliable data are not available for a countryorregion, the estimation has been based on:

(i) reported incidence of all diarrhoeal diseases in infants and children, when the disease in question is related to diarrhoeal diseases. Table 2 shows the distribution of pathogens frequently identified in children with acute diarrhoea seen at treatment centres in developing countries;

and/or

(ii) extrapolation from other regions, taking into account the likelihood of under- reporting, the nature of the disease, the foods eaten in the region, and the general standard of food safety as compared to the regions where data are available.

The following examples illustrate how the semi- quantitative estimations of foodborne disease occurrence have been carried out.

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CD Table 1 Estimation of occurrence of diseases which are or may be foodborne, WHO Regions Tableau 1 Estimation de Ia frequence des maladies d'origine alimentaire certaine ou supposee, par Region OMS AMR WPR Diseases•-Maladies• AFR North Center & EMR EURb SEAR New-Zealand, Australia Autres parties Nord South Centre & Japan Other Parts & Sud Nlle-Zelande, Australle & Japan Bacterial infections and intoxications -Taxi-infections bacteriennes Bacillus cereus gastroenteritis -Gastro-enterite ~ Bacillus cereus +++ ++ +++ +++ ++ +++ ++ +++ Botulism-Botulisme + + + + + + + + Brucellosis -Brucellose +lt+C + ++ +lt+C -f+I++C +lt+C + +I++C Campylobacteriosis-Campylobacteriose +++ ++ +++ +++ ++ +++ ++ +++ Cholera -Cholera +/t+C -1+ +ft+C +

-

+ -1+ + Clostridium perfringens enteritis -Enterite ~ Clostridium pertringens +++ ++ +++ +++ ++ +++ ++ +++ Escherichia coli disease -Maladies ~ Escherichia coli +++ + +++ +++ +I++C +++ + +++ Listeriosis -Listeriose + + + + + + + + Typhoid and paratyphoid fevers -Typho"ide et paratypho"ide ++ + ++ ++ + ++ + ++ Salmonellosis -Salmonellose +++ ++ +++ +++ ++l+++c +++ ++ +++ Shigellosis -Shigellose +++ ++ +++ +++ +I++C +++ ++ +++ Staphylococcus aureus intoxication -Intoxication par Staphylococcus au reus +++ ++ +++ +++ ++ +++ ++ +++ Vibrio parahaemolyticus enteritis -Enterite ~ Vibrio parahaemolyticus + + ++ +I++C ++ Vibrio vulnificus septicemia -Septicemie ~ Vibrio vulnificus + +lt+C +/t+C ++ Yersiniosis -Yersiniose + +I++C + ~ ~ Viral infections -Infections virales

s

Hepatitis A -Hepatite A ++ ++ ++ ++ ++ ++ ++ ++ ::!"

m

Norwalk virus gastroenteritis-Gastro-enterite ~virus de Norwalk + + + + + + + + ,....

~

Poliomyelitis -Poliomyelite ++ + + + + ++ + +I++ ,.... Rotavirus gastroenteritis -Gastro-enterite ~ rotavirus +++ ++ +++ +++ ++ +++ ++ +++ ~ Protozoa infections -Infections

a

protozoa ires 1'1:

~

Amoebiasis -Amibiase +++ + +++ ++I+++ + +++ + +++ ~

-

Cryptospridiosis-Cryptospridiose +++ ++ +++ +++ ++ +++ ++ +++

g:

... Giardiasis -Giardiase +++ ++ +++ ++I+++ +lt+C +++ ++ +++

i8

Toxoplasmosis-Toxoplasmose ++ + ++ +I++ + +I++ ++ ++ -::::!

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~ ,..

§

~

,.... ~

r-

81 -..

i8

-:::::! <D

Diseases•-Maladiesa Ascariasis -Ascaridiase Clonorchiasis -Clonorchiase Fascioliasis -Distomatose Hydatidosis -Hydatidose Opisthorchiasis (0. felineus)-Opisthorchiase (0. felineus) Opisthorchiasis ( 0. viverrim) -Opisthorchiase ( 0. viverrim) Taeniasis/cystocercosis -Teniaselcysticercose Trichinellosis -Trichinose Trichuriasis -Trichoc6phalose

AFR +++ -I++C +I++C +l+++c +I++ +++

AMR North Center & Nord South Centre & Sud Helminthiasis -Helminthiases + + + +

+++ ++l+++c ++ +I++ +++ a not occurring-absente;+ occasional or rare-occasionnelle ou rare;++ frequent-fr~quente; +++very frequent-Ires frequente.

EMR +++ ++ +I++ + -I+C +++

EURb SEAR +I++C +++ -I++C

-

-l+++c

-

+ -l+++c -f+++c + +I++C +I++C +I++C +++

WPR New-Zealand, Australia Autres parties & Japan Other Parts Nlle-Zelande, Australie & Japon +I++ +++ -I+C ++l+++c

-

-I++ + +l+++c +I++ ++ ++ ++ b Armenia, Azarbaijan, Georgia, Kazakstan, Kyrgystan, Tadjikistan, Turkmenistan and Uzbekistan are included in EMR or SEAR-L'Armt!nie, I'Azerbaidjan, Ia Gt!orgie,le Kazakstan, le Kirghizistan, le Tadjikistan, le Turkmenistan etl' Ouzbt!kistan, son! compris dans SEAR et EMR. c Great regional variations-lmportantes variations r~gionales.

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Table 2

Pathogens frequently identified in children with acute diarrhoea seen at treatment centres in developing countries TIIIIIIU 2

Agents pathogimes frequemment identifies chez les enfants atteints de diarrhee aigue vus dans les centres de soins dans les pays en developpement

Pathogen- Pathogene

Rotavirus Escherichia coli

- enterotoxigenic - enterotoxinogene - enteropathogenic - enteropathogene Shigella spp.

Campy/obacter jejuni

Vibrio cho/erae 01

Salmonella (non typhi) Cryptosporidium

Soun:e: Ref- Ref. (7)

%

15-25 10-20 1-5 5-15 10-15

5-10 1-5 5-15

Botulism: Although mild cases do occur, the disease usually has severe health consequences. Se- verely affected persons would seek medical advice.

The degree of under-reporting is likely to be lower than for other diseases. The incidence of this disease is reported by a number of countries, and data are available in national epidemiological surveillance programmes. Scientific literature is also a source of data for many countries. The microor- ganism is ubiquitous in nature and can therefore occur all over the world. Although a proportion of cases may remain unreported, available data justify classifying this disease as a rare or occasional world- wide.

Brucellosis: This is a severe disease which is notifiable in numerous countries; its incidence has decreased in European and North American countries as a result of veterinary measures and the pasteurization of milk. In some southern Euro- pean countries e.g. Italy, France, Spain and Greece, where the traditional production of soft cheese from raw milk and the consumption of raw milk are still common, the disease has a higher level of occurrence. In developing countries where milk pasteurization is not yet systematic, the disease also occurs with higher frequency than in industrialized countries. Based on available information, the disease is classified as rare in most industrialized countries and frequent in developing countries, in particular in the Eastern Mediterra- nean Region.

Cholera: Regarded as severe, this disease is subject to international notification. The estimation of its occurrence is based on the number of notified cases. Based on the reported data, cholera is esti- 10

mated to be a rare to frequent disease, depending on the region.

Campylobacteriosis, salmonellosis, shigellosis:

Data on incidence are available from a number of industrialized countries (e.g. Japan, Australia, United States of America, and several European countries). Their global incidence in most developing countries is unknown. However their etio- logical agents are among the most important for diarrhoeal diseases in infants and children as well as for travellers' diarrhoea. Therefore, for countries or regions where data on these diseases are not available, the calculation is based on the estimated number of episodes of diarrhoeal diseases in infants and children and travellers' diarrhoea.

Escherichia coli infections: Their incidence in most countries is unknown. Data from a few industrialized countries point to a relatively low occurrence compared to other foodborne infections and to other regions. They are therefore classified as rare or occasional in industrialized regions. How- ever, pathogenic strains of E. coli are the leading cause of diarrhoeal diseases in developing regions.

They are thus estimated to occur very frequently in regions where diarrhoeal diseases are highly preva- lent.

Staphylococcus aureus intoxication, Bacillus cereus gastroenteritis, Clostridium perfringens enteritis: These diseases are reported in several countries under the general term food poisoningc. Their occurrence is highly underestimated because they are often mild and self-limiting. Some laboratories may also choose not to look for these agents. Therefore, although the reported incidence in industrialized countries would indicate that these diseases should be classified as rare or occasional, it is likely that they occur frequently. Where data are not available, pre- dicted occurrence is based on data from other regions, taking into account the food safety standards of the region under study in comparison to the region where data are available.

Rotavirus gastroenteritis: Although its incidence is unknown, it is one of the major causes of diarrhoeal diseases, occurring in both industrialized and developing countries.

Amoebiasis: Its incidence is reported by a few countries only. In regions where the incidence is unknown, the estimation is based on comparison with regions having similar standards of food safety.

Cryptosporidiosis, Giardiasis: Incidence is reported by a number of countries, are also available data and literature. They are frequently the cause of diarrhoeal diseases in both industrialized and de-

c The term 'food poisoning' is ill-defined and non-scientific; its use is discouraged by WHO.

Rapp. trimest. statist. sanff. mond., 50 (1997)

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veloping countries. In the former, both infections are frequently associated with waterborne outbreaks.

Conclusion

Weaknesses and variations in foodborne disease surveillance systems, where such programmes exist, make a global estimation of foodborne diseases difficult. However, such data are essential for raising awareness about existing problems, setting priority food safety measures, using resources in a cost-effective way, and evaluating the impact of measures. At the national level, countries should consider developing or strengthening their foodborne disease investigation and surveillance sys- tem. At the international level, there is need to provide further guidance in investigation and surveillance and to harmonize reporting systems.

Therefore, although an exact global estimation is not possible because of uncertainty about information or lack of data, it is possible, by using a number assumptions, to provide a picture of the occurrence of food borne diseases on a semi-quantitative scale in various regions of the world.

Acknowledgements

The authors gratefully acknowledge the contribu- tion of the following persons in reviewing the manuscript: Dr Anthony Hazzard, University of Western Sydney, New South Wales, Australia;

Dr KE. Mott, Division of control of Tropical Dis- eases, World Health Organization, Geneva, Switzerland; Dr Morris E. Potter, Centers for Dis- ease Control, Atlanta, USA; Dr L. Savioli, Division of control of Tropical Diseases, World Health Or- ganization, Geneva, Switzerland; Dr M.C. Thuri- aux, Division of Emerging and other Communica- ble Diseases Surveillance and Control, World Health Organization, Geneva, Switzerland; and Dr Ewen C.D. Todd, Health Canada, Ottawa, Ontario, Canada.

Summary

Foodborne diseases are one of the most widespread health problems, but because of weaknesses in foodborne disease surveillance and variation in reporting

Wid hffh statist. quart., ^{50 (1997)}

systems between countries, it is difficult to make an estimation of their true incidence. This paper describes the constraints in the collection of information on the incidence and/or prevalence of foodborne diseases, including investigation and reporting at national and international levels. It also makes an attempt to semi- quantify the occurrence of food borne diseases of micro- bial and parasitical origin in different regions of the world.

Resume

Estimation mondiale des maladies d'origine ali menta ire

Les maladies d'origine alimentaire sont l'un des problemes de sante les plus repandus, mais il est difficlle d'en evaluer !'incidence vraie en raison de Ia faiblesse des systemes de surveillance et des differences entre les modalites de notification des cas d'un pays

a

l'autre. Cet article decrit les problemes qui se posen! au niveau de Ia collecte des Informations sur !'incidence et/ou Ia prevalence des malad1es d'ongine alimentaire, de !'investigation et de Ia notification aux niveaux national et international. II tente egalement d'evaluer de fac;:on semi-quantitative Ia frequence des maladies d'origine alimenta1re microbiennes et parasitaires dans differen- tes parties du monde.

References - Reference

I. WHO Technical Report Series, No. 705. 1984. ( Theroleoffood safety in health and development: report of a joint FAO/WHO Expert Committee on Food Safety).

OMS Serie de rapports techniques, N° 705, 1985 (La securite des produzts alimentaires et son role dans La sante et le dtiveloppement:rapportd'un Comite d'experts FAO/OMS de Ia securite des produits alimentaires).

2. Norling, B. Food Poisoning in Sweden: results of a field study.

Report No. 41/94. National Food Administration, Uppsala, Sweden, 1994.

3. Todd, E.C.D. Preliminary Estimates of Costs of Food borne Disease in the United States. journal of food protection, 52(8):

586-594 ( 1989).

4. Notennans, S. & Hooenboom-Verdegall, A.S. Existing and emerging food borne diseases. International JOUrnal of food murobiology, 15: 197-205 ( 1992).

5. Notennans, S. & Van de Giessen. Food borne diseases in the 1980s and 1990s. Food contra~ 4(3):122-124 (1993).

6. Hodges, I. Raw to cooked food, Communzty awareness of safe food handling practices, Wellington, Ministry of Health, 1993.

7. World Health Organization. Readings on diarrhoea, student manual. Geneva, WHO, 1992.

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