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Vaccination priorities
International Journal of Antimicrobial Agents 21 (2003) 175 /180 www.isochem.org
Vaccination priorities Robert Steffen *, Ana Ban˜os, Chiara deBernardis World Health Organization Collaborating Centre for Travellers’ Health, Institute of Social and Preventive Medicine (ISPM), University of Zurich, Sumatrastrasse 30, CH-8006 Zurich, Switzerland
Abstract Selection of immunizations should be based on requirements and on risk of infection. According to the International Health Regulations, many countries require yellow fever vaccination and proof thereof as the International Certificate of vaccination. Additionally selected countries require proof of vaccination against cholera and meningococcal disease. A consultation for travel health advice is always an opportunity to ascertain that routine immunizations have been performed. Recommended immunizations often are more important for traveller’s health than the required or routine ones. The most frequent vaccine preventable infection in non-immune travellers to developing countries is hepatitis A with an average incidence rate of 0.3% per month; in high risk backpackers or foreign-aid-volunteers this rate is 2.0%. Many immunizations are recommended for special risk groups only: there is a growing tendency in many countries to immunize all young travellers to developing countries against hepatitis B, as it is uncertain who will voluntarily or involuntarily get exposed. The attack rate of influenza in intercontinental travel is estimated to be 1%. Immunity against poliomyelitis remains essential for travel to Africa and parts of Asia. Many of the 0.2 /0.4% who experience an animal bite are at risk of rabies. Typhoid fever is diagnosed with an incidence rate of 0.03% per month among travellers to the Indian subcontinent, North and West Africa (except Tunisia), and Peru, elsewhere this rate is 10-fold lower. Meningococcal disease, Japanese encephalitis, cholera and tuberculosis have been reported in travellers, but these infections are rare in this population. Although no travel health vaccine is cost beneficial, most professionals will offer protection against the frequent risks, while most would find it ridiculous to use all available vaccines in every traveller. It is essentially an arbitrary decision made on the risk level one wishes to recommend protection / /but the priorities need to be set correctly. # 2002 Elsevier Science B.V. and the International Society of Chemotherapy. All rights reserved. Keywords: Immunization; Risk levels; Special risk groups
1. Introduction The epidemiological data of the various vaccine preventable infections will be discussed as three groups: those required, routine and those recommended. A caveat first: on most vaccine preventable diseases no recent morbidity and mortality data exist and there are indications that the incidence rates identified in 1970s and 1980s may be decreasing. It is uncertain to what degree this is due to improved hygienic conditions at the destination/ /a contradiction when travellers’ diarrhoea is considered / /or to immunization [1]. It is unlikely that the current risk in travellers can be studied,
* Corresponding author. Tel.: /41-1-634-4621; fax: /41-1-6344984 E-mail address: [email protected] (R. Steffen).
as ethically, it is impossible to leave cohorts unprotected for an epidemiological assessment.
2. Required procedures Yellow fever occurs only in tropical Africa and Northern South America (Fig. 1) and usually a few hundred cases are reported to WHO annually but it is estimated that more than 200 000 cases occur. Yellow fever has never occurred in Asia although the vectors, Aedes and Haemagogus have been observed there. Yellow fever is extremely rare in travellers, but several cases in unvaccinated travellers have been reported in the last 10 years despite the fact these travellers should have been immunized [2]. All four travellers recently reported with yellow fever died (Fig. 1). Cholera and plague would be the other two diseases subject to current valid International Health Regula-
0924-8579/02/$30 # 2002 Elsevier Science B.V. and the International Society of Chemotherapy. All rights reserved. PII: S 0 9 2 4 - 8 5 7 9 ( 0 2 ) 0 0 2 8 6 - 8
176
R. Steffen et al. / International Journal of Antimicrobial Agents 21 (2003) 175 /180
Fig. 1. Yellow fever endemic countries and recent cases of yellow fever in travellers.
Fig. 2. Polio situation, 2001.
R. Steffen et al. / International Journal of Antimicrobial Agents 21 (2003) 175 /180
177
Table 1 Rationale and prioritization for immunization of travellers Infection
Hepatitis A Hepatitis B Rabies Yellow fever Typhoid fever Influenza Poliomyelitis Diphtheria Tetanus Meningococcal disease Japanese encephalitis Cholera Measles
Incidence
/// // // (/) // //(/)? (/) (/) (/) (/) (/) / (/)
Impact
// /// // /// / (/) // // // // // / /
Total
Immunization
///// ///// //// ///(/) /// /// //(/) //(/) //(/) //(/) //(/) // /(/)
Yes
No
Illogical The overcautions, unconcerned about AE
Rational The hazardous, the cost conscious
Impact (rate per 100 000): ///: high case fatality rate, serious residuals ( /100); //: /5% case fatality rate or incapacitation /4 weeks (1 / 99); /: low case fatality rate, brief incapacitation (0.1 /0.9); (/): B/0.1.
Table 2 Comparison of various expert recommendations for immunizations in non-immune travellers planning to stay in a developing country Expert group
WHO World
CATMAT Canada
CDC USA
PHLS UK
NHMRC Australia
Required Yellow fever
**
**
**
**
**
Routine Diphtheria/tetanus Poliomyelitis Measles
*** ** ***
*** ** ***
*** ** ***
*** ** ***
*** ** ***
Recommended Hepatitis A Hepatitis B Rabies Typhoid fever Meningococcal Japanese encephalitis Tuberculosis Cholera Influenza
*** * * * * * * / *
*** * * * * * //* / *
*** * * * * * / //* ?
***/* * * * * * * / *
***/* * * * * * * / ?
***, all; **, all when visit is to endemic country; *, risk group only; /, none.
tions, but since immunization is required very rarely, this will be discussed below. Meningococcal disease has frequently been observed during or after the Hajj or Umrah pilgrimage to Mecca (200/100 000), but it is rare even in travellers staying in countries where the infection is highly endemic (0.04/ 100 000) [3]. The case fatality rate among travellers slightly exceeds 20%. Rarely, Neisseria meningitidis may be transmitted during air-travel of at least 8 h duration [4].
3. Routine procedures To our knowledge no cases of tetanus have been recently reported in travellers, but such reports may be hidden in national surveillance data. As demonstrated by a large epidemic in the former Soviet Union 1990 /1997, diphtheria may flare up under specific circumstances [5]. This epidemic resulted in dozens of importations to Western Europe and North America and some travellers died while still in Russia.
178
R. Steffen et al. / International Journal of Antimicrobial Agents 21 (2003) 175 /180
Table 3 Recommended vaccines: the risk criteria Vaccine
Time
Environmental factor
Host factor
Yellow fever Hepatitis B Rabies Typhoid Meningococcal Japanese encephalitis Encephalitis-tick borne Tuberculosis Cholera Influenza
/ /1 month (WHO) /1 month (WHO) /1 month (Steffen) / /2 /4 weeks / / / /
Endemic region, mainly rural High (intermediate) endemicity High(er) endemicity ‘Recognized risk’ (CDC). ‘off tourist itinerary’ (CDC) Epidemics, meningitis belt (dry) Rural areas in season Endemic, forested areas Very remote areas (CDC none) Work in refugee camp Many long flights (?)
/ Ambitious for contacts Young/male/activity/etc. Gastric anacidity / / / Infants and children (Gastric anacidity) /65 year, pre-existing disease
The far less serious form of cutaneous diphtheria is occasionally imported, mainly from developing countries [6]. Poliomyelitis, although almost eradicated from most parts of the world (Fig. 2) may rarely still be associated with virus imported by asymptomatic persons, as demonstrated recently in Bulgaria and China [7,8]. In travellers, poliomyelitis has not been observed since the 1990s (Fig. 2). Hardly any data exist on pertussis, Haemophilus influenzae B, measles, mumps and rubella in travellers. Because of suboptimal compliance with vaccination, European, African and Asian travellers are responsible for outbreaks on the American continent, where vaccine uptake is far superior [9]. It has been shown that hepatitis B, now a routine immunization in most industrialised countries, is mainly a problem for expatriates living close to the local population and for travellers breaking the most basic hygienic rules. The monthly incidence is 25/100 000 for symptomatic infections and 80 /420/100 000 for all infections [10]. Transmission relies on only very low numbers of virus and the exact mode of transmission may remain undetectable in many individuals but clear risk factors, such as casual sex, nosocomial transmission [11], etc. have often been suspected. Behavioural surveys have shown that 10 /15% of travellers voluntarily or involuntarily expose themselves to blood and body fluids while abroad in high risk countries [12,13]. Besides the risk factors mentioned above such persons have been reported as visiting a dental hygienist, or having acupuncture, cosmetic surgery, tattoos, ear piercing, scarification, etc.
4. Recommended procedures The most frequent vaccine preventable infection in non-immune travellers to developing countries is hepa-
titis A with an average incidence rate of 300/100 000 per month; in high risk backpackers or foreign-aid-volunteers this rate is 2000/100 000 [14]. In various studies reviewed it has been shown that tourists staying in luxury hotels at multistar resorts may also be at risk of infection. It should be noted that the Asian and African regions bordering the Mediterranean and the Caribbean are rated as destinations ‘with moderate to high risk of infection’ by WHO [15]. Travellers to these destinations are often not complying with hepatitis A vaccination recommendations. Those visiting friends and relatives (VFRs) are particularly negligent. Several hepatitis A epidemics originated from such food handlers and from children attending kindergartens. Typhoid fever is diagnosed with an incidence rate of 30/100 000 per month among travellers to the Indian subcontinent, North and West Africa (except Tunisia), and Peru; elsewhere this rate is 10-fold lower [16 /18]. A fair proportion of infections is imported by VFRs, but people originating in industrialised countries are also affected. The case fatality rate was usually 0 /1% among travellers. The risk of rabies is particularly high in Asia from where 90% of all human rabies deaths are reported [19], but there may be under-reporting in other parts of the world. Rabies free areas include Australia, New Zealand, the Pacific Islands, Scandinavia, the United Kingdom, Ireland, Iceland and Switzerland. In developing countries many of the 0.2 /0.4% who each month are reported to have had an animal bite, are at risk of rabies [20,21]. Rabies is a risk particularly in those who are in close contact with native animals over a prolonged time, e.g. missionaries, those en route with bikes, small children, people working with animals or those who explore caves [22]. Basing on post-travel skin tests, the incidence rate of M . tuberculosis infections is 3000/100 000 personmonths of travel and 60/100 000 had active tuberculosis [23]. The prevalence of transmissible tuberculosis among
R. Steffen et al. / International Journal of Antimicrobial Agents 21 (2003) 175 /180
air travellers is estimated to be 5 /100/100 000 passengers, depending on the route of the plane. Nevertheless, transmission in flight or during prolonged train and bus rides have only rarely been reported and outdoor transmission might be ignored unless there is repeated exposure, as it may occur particularly among long-term, low-budget travellers or expatriates [24]. The risk of cholera is approximately 0.2/100 000, although asymptomatic and oligosymptomatic infections may be more frequent, as demonstrated in Japanese travellers [25,26]. The case fatality rate is less than 2% among travellers. For several potentially vaccine preventable diseases the risk of infection is less than 1 per million. Although a few dozen cases of Japanese encephalitis have been diagnosed in civilian travellers within the last 25 years, the attack rate in civilians is less than 1 per million because of the number of travellers. Exceptionally a short-term tourist in Bali was affected [27]. Only two international travellers have been diagnosed with plague since 1966. Very few anecdotal reports have documented tick borne encephalitis in international travellers, although the disease occurs in persons hiking or camping in endemic areas. So far no data have been published on the risk of influenza in this population, but various outbreaks on cruise ships or after a flight have been described.
5. Conclusions From the epidemiological basis described above, it is clear that future travellers should receive: All required immunizations. If health professionals do not comply with this rule, serious problems may arise as a traveller may be refused entry to the country, or he may be quarantined or immunized at the airport upon arrival. Often a fine has to be paid. All routine immunizations, based on the various national programmes. The appropriate recommended immunizations. The art of travel medicine is not to give all available vaccines */this would result in unnecessary costs and adverse events / /but to make the correct arbitrary decision how far down the priority list (Table 1) he should recommend protection. It is certainly wrong to protect a traveller against rare and less serious infections, while leaving him or her at risk of those more frequent and more serious. As shown in Table 2, the expert authorities in most countries and at WHO have a similar rating related to travel vaccines, the crucial matter is to detect pre-travel who belongs to the ‘risk groups’. Table 3 describes the characteristics to be considered. One should, however, not only consider environmental and travel characteristics as host factors may also
179
play a role. For instance it is useless to immunize persons against hepatitis A who already have acquired lifelong immunity by infection. This is often the case in those from the lower socio-economic strata of developing countries or after the history of jaundice, or in persons who have been born before World War II anywhere in the world.
References [1] Steffen R. Despite good tools we do not effectively reduce travelers’ Hepatitis A. J Travel Med 2002;9:1 /2. [2] (Anonymous). Yellow fever, 1998 /1999. WHO Wkly Epidemiol Rec 2000;40:322 /328. [3] Koch S, Steffen R. Meningococcal disease in travelers: vaccination recommendations. J Travel Med 1994;1:4 /7. [4] (Anonymous). Exposure to patients with meningococcal disease on aircrafts /United States, 1999 /2001. MMWR 2001;50:485 / 489. [5] Galazka A. The changing epidemiology of diphtheria in the vaccine era. J Infect Dis 2000;181(Suppl 1):2 /9. [6] (Anonymous). Diphtheria in visitors to Africa. CDR wkly 1998;8:289. [7] (Anonymous). Imported wild poliovirus causing poliomyelitis, Bulgaria. WHO Wkly Epidemiol Rec 2001;76:332 /335. [8] (Anonymous). Wild poliovirus imported into Qinghai province, China. WHO Wkly Epidemiol Rec 2000;75:55 /57. [9] Rota JS, Rota PA, Redd SB, et al. Genetic analysis of measles viruses isolated in the United States, 1995 /1996. J Infect Dis 1998;177:204 /8. [10] Lo¨scher T, Keystone JS, Steffen R. Vaccination of travelers against Hepatitis A and B. J Travel Med 1999;6:107 /14. [11] Simonsen L, Kane A, Lloyd J, et al. Unsafe injections in the developing world and transmission of bloodborne pathogens: a review. Bull WHO 1999;77:789 /800. [12] Zuckerman JN, Steffen R. Risk of hepatitis B in travelers as compared to immunization status. J Travel Med 2000;7:170 /4. [13] Correia JD, Shafer RT, Patel V, et al. Blood and body fluid exposure as a health risk for international travelers. J Travel Med 2001;8:263 /6. [14] Steffen R, Kane MA, Shapiro CN, et al. Epidemiology and prevention of hepatitis A in travelers. JAMA 1994;272:885 /9. [15] World Health Organisation (WHO). International travel and health. Geneva, Switzerland, 2002. [16] Steffen R. Typhoid vaccine, for whom? Lancet 1982(i):615 /6. [17] Mermin JH, Townes JM, Gerber M. Typhoid fever in the United States, 1985 /1994. Arch Intern Med 1998;158:633 /8. [18] Caumes E, Ehya N, Nguyen J, et al. Typhoid and paratyphoid fever: a 10-year retrospective study of 41 cases in a Parisian hospital. J Travel Med 2001;8:293 /7. [19] (Anonymous). Rabies, Asia. WHO Wkly Epidem Rec 2001;76:320 /323. [20] Bernard KW, Fishbein DB. Pre-exposure rabies prophylaxis for travellers: are the benefits worth the cost? Vaccine 1991;9:833 /6. [21] Hatz CF, Bidaux JM, Eichenberger K, et al. Circumstances and management of 72 animal bites among long-term residents in the tropics. Vaccine 1995;13:811 /5. [22] Haupt W. Rabies */risk of exposure and current trends in prevention of human cases. Vaccine 1999;17:1742 /9. [23] Cobelens FGJ, van Deutekom H, Draayer-Jansen IWE, et al. Risk of infection with Mycobacterium tuberculosis in travellers to areas of high tuberculosis endemicity. Lancet 2000;356:461 /5. [24] Rieder HL. Risk of travel-associated tuberculosis. Clin Infect Dis 2001;33:1393 /6.
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[25] Taylor DN, Rizzo J, Meza R, et al. Emergence of Mycobacterium kansasii as the leading mycobacterial pathogen isolated over a 20year period at a mid-western veterans affairs hospital. Clin Infect Dis 1996;22:1109 /10.
[26] Wittlinger F, Steffen R, Watanabe H, et al. Risk of cholera among western and Japanese travelers. J Travel Med 1995;2:154 /8. [27] Wittesjo¨ B, Eitrem R, Niklasson B, et al. Japanese encephalitis after a 10-day holiday in Bali. Lancet 1995;345:856.
Vaccination priorities Robert Steffen *, Ana Ban˜os, Chiara deBernardis World Health Organization Collaborating Centre for Travellers’ Health, Institute of Social and Preventive Medicine (ISPM), University of Zurich, Sumatrastrasse 30, CH-8006 Zurich, Switzerland
Abstract Selection of immunizations should be based on requirements and on risk of infection. According to the International Health Regulations, many countries require yellow fever vaccination and proof thereof as the International Certificate of vaccination. Additionally selected countries require proof of vaccination against cholera and meningococcal disease. A consultation for travel health advice is always an opportunity to ascertain that routine immunizations have been performed. Recommended immunizations often are more important for traveller’s health than the required or routine ones. The most frequent vaccine preventable infection in non-immune travellers to developing countries is hepatitis A with an average incidence rate of 0.3% per month; in high risk backpackers or foreign-aid-volunteers this rate is 2.0%. Many immunizations are recommended for special risk groups only: there is a growing tendency in many countries to immunize all young travellers to developing countries against hepatitis B, as it is uncertain who will voluntarily or involuntarily get exposed. The attack rate of influenza in intercontinental travel is estimated to be 1%. Immunity against poliomyelitis remains essential for travel to Africa and parts of Asia. Many of the 0.2 /0.4% who experience an animal bite are at risk of rabies. Typhoid fever is diagnosed with an incidence rate of 0.03% per month among travellers to the Indian subcontinent, North and West Africa (except Tunisia), and Peru, elsewhere this rate is 10-fold lower. Meningococcal disease, Japanese encephalitis, cholera and tuberculosis have been reported in travellers, but these infections are rare in this population. Although no travel health vaccine is cost beneficial, most professionals will offer protection against the frequent risks, while most would find it ridiculous to use all available vaccines in every traveller. It is essentially an arbitrary decision made on the risk level one wishes to recommend protection / /but the priorities need to be set correctly. # 2002 Elsevier Science B.V. and the International Society of Chemotherapy. All rights reserved. Keywords: Immunization; Risk levels; Special risk groups
1. Introduction The epidemiological data of the various vaccine preventable infections will be discussed as three groups: those required, routine and those recommended. A caveat first: on most vaccine preventable diseases no recent morbidity and mortality data exist and there are indications that the incidence rates identified in 1970s and 1980s may be decreasing. It is uncertain to what degree this is due to improved hygienic conditions at the destination/ /a contradiction when travellers’ diarrhoea is considered / /or to immunization [1]. It is unlikely that the current risk in travellers can be studied,
* Corresponding author. Tel.: /41-1-634-4621; fax: /41-1-6344984 E-mail address: [email protected] (R. Steffen).
as ethically, it is impossible to leave cohorts unprotected for an epidemiological assessment.
2. Required procedures Yellow fever occurs only in tropical Africa and Northern South America (Fig. 1) and usually a few hundred cases are reported to WHO annually but it is estimated that more than 200 000 cases occur. Yellow fever has never occurred in Asia although the vectors, Aedes and Haemagogus have been observed there. Yellow fever is extremely rare in travellers, but several cases in unvaccinated travellers have been reported in the last 10 years despite the fact these travellers should have been immunized [2]. All four travellers recently reported with yellow fever died (Fig. 1). Cholera and plague would be the other two diseases subject to current valid International Health Regula-
0924-8579/02/$30 # 2002 Elsevier Science B.V. and the International Society of Chemotherapy. All rights reserved. PII: S 0 9 2 4 - 8 5 7 9 ( 0 2 ) 0 0 2 8 6 - 8
176
R. Steffen et al. / International Journal of Antimicrobial Agents 21 (2003) 175 /180
Fig. 1. Yellow fever endemic countries and recent cases of yellow fever in travellers.
Fig. 2. Polio situation, 2001.
R. Steffen et al. / International Journal of Antimicrobial Agents 21 (2003) 175 /180
177
Table 1 Rationale and prioritization for immunization of travellers Infection
Hepatitis A Hepatitis B Rabies Yellow fever Typhoid fever Influenza Poliomyelitis Diphtheria Tetanus Meningococcal disease Japanese encephalitis Cholera Measles
Incidence
/// // // (/) // //(/)? (/) (/) (/) (/) (/) / (/)
Impact
// /// // /// / (/) // // // // // / /
Total
Immunization
///// ///// //// ///(/) /// /// //(/) //(/) //(/) //(/) //(/) // /(/)
Yes
No
Illogical The overcautions, unconcerned about AE
Rational The hazardous, the cost conscious
Impact (rate per 100 000): ///: high case fatality rate, serious residuals ( /100); //: /5% case fatality rate or incapacitation /4 weeks (1 / 99); /: low case fatality rate, brief incapacitation (0.1 /0.9); (/): B/0.1.
Table 2 Comparison of various expert recommendations for immunizations in non-immune travellers planning to stay in a developing country Expert group
WHO World
CATMAT Canada
CDC USA
PHLS UK
NHMRC Australia
Required Yellow fever
**
**
**
**
**
Routine Diphtheria/tetanus Poliomyelitis Measles
*** ** ***
*** ** ***
*** ** ***
*** ** ***
*** ** ***
Recommended Hepatitis A Hepatitis B Rabies Typhoid fever Meningococcal Japanese encephalitis Tuberculosis Cholera Influenza
*** * * * * * * / *
*** * * * * * //* / *
*** * * * * * / //* ?
***/* * * * * * * / *
***/* * * * * * * / ?
***, all; **, all when visit is to endemic country; *, risk group only; /, none.
tions, but since immunization is required very rarely, this will be discussed below. Meningococcal disease has frequently been observed during or after the Hajj or Umrah pilgrimage to Mecca (200/100 000), but it is rare even in travellers staying in countries where the infection is highly endemic (0.04/ 100 000) [3]. The case fatality rate among travellers slightly exceeds 20%. Rarely, Neisseria meningitidis may be transmitted during air-travel of at least 8 h duration [4].
3. Routine procedures To our knowledge no cases of tetanus have been recently reported in travellers, but such reports may be hidden in national surveillance data. As demonstrated by a large epidemic in the former Soviet Union 1990 /1997, diphtheria may flare up under specific circumstances [5]. This epidemic resulted in dozens of importations to Western Europe and North America and some travellers died while still in Russia.
178
R. Steffen et al. / International Journal of Antimicrobial Agents 21 (2003) 175 /180
Table 3 Recommended vaccines: the risk criteria Vaccine
Time
Environmental factor
Host factor
Yellow fever Hepatitis B Rabies Typhoid Meningococcal Japanese encephalitis Encephalitis-tick borne Tuberculosis Cholera Influenza
/ /1 month (WHO) /1 month (WHO) /1 month (Steffen) / /2 /4 weeks / / / /
Endemic region, mainly rural High (intermediate) endemicity High(er) endemicity ‘Recognized risk’ (CDC). ‘off tourist itinerary’ (CDC) Epidemics, meningitis belt (dry) Rural areas in season Endemic, forested areas Very remote areas (CDC none) Work in refugee camp Many long flights (?)
/ Ambitious for contacts Young/male/activity/etc. Gastric anacidity / / / Infants and children (Gastric anacidity) /65 year, pre-existing disease
The far less serious form of cutaneous diphtheria is occasionally imported, mainly from developing countries [6]. Poliomyelitis, although almost eradicated from most parts of the world (Fig. 2) may rarely still be associated with virus imported by asymptomatic persons, as demonstrated recently in Bulgaria and China [7,8]. In travellers, poliomyelitis has not been observed since the 1990s (Fig. 2). Hardly any data exist on pertussis, Haemophilus influenzae B, measles, mumps and rubella in travellers. Because of suboptimal compliance with vaccination, European, African and Asian travellers are responsible for outbreaks on the American continent, where vaccine uptake is far superior [9]. It has been shown that hepatitis B, now a routine immunization in most industrialised countries, is mainly a problem for expatriates living close to the local population and for travellers breaking the most basic hygienic rules. The monthly incidence is 25/100 000 for symptomatic infections and 80 /420/100 000 for all infections [10]. Transmission relies on only very low numbers of virus and the exact mode of transmission may remain undetectable in many individuals but clear risk factors, such as casual sex, nosocomial transmission [11], etc. have often been suspected. Behavioural surveys have shown that 10 /15% of travellers voluntarily or involuntarily expose themselves to blood and body fluids while abroad in high risk countries [12,13]. Besides the risk factors mentioned above such persons have been reported as visiting a dental hygienist, or having acupuncture, cosmetic surgery, tattoos, ear piercing, scarification, etc.
4. Recommended procedures The most frequent vaccine preventable infection in non-immune travellers to developing countries is hepa-
titis A with an average incidence rate of 300/100 000 per month; in high risk backpackers or foreign-aid-volunteers this rate is 2000/100 000 [14]. In various studies reviewed it has been shown that tourists staying in luxury hotels at multistar resorts may also be at risk of infection. It should be noted that the Asian and African regions bordering the Mediterranean and the Caribbean are rated as destinations ‘with moderate to high risk of infection’ by WHO [15]. Travellers to these destinations are often not complying with hepatitis A vaccination recommendations. Those visiting friends and relatives (VFRs) are particularly negligent. Several hepatitis A epidemics originated from such food handlers and from children attending kindergartens. Typhoid fever is diagnosed with an incidence rate of 30/100 000 per month among travellers to the Indian subcontinent, North and West Africa (except Tunisia), and Peru; elsewhere this rate is 10-fold lower [16 /18]. A fair proportion of infections is imported by VFRs, but people originating in industrialised countries are also affected. The case fatality rate was usually 0 /1% among travellers. The risk of rabies is particularly high in Asia from where 90% of all human rabies deaths are reported [19], but there may be under-reporting in other parts of the world. Rabies free areas include Australia, New Zealand, the Pacific Islands, Scandinavia, the United Kingdom, Ireland, Iceland and Switzerland. In developing countries many of the 0.2 /0.4% who each month are reported to have had an animal bite, are at risk of rabies [20,21]. Rabies is a risk particularly in those who are in close contact with native animals over a prolonged time, e.g. missionaries, those en route with bikes, small children, people working with animals or those who explore caves [22]. Basing on post-travel skin tests, the incidence rate of M . tuberculosis infections is 3000/100 000 personmonths of travel and 60/100 000 had active tuberculosis [23]. The prevalence of transmissible tuberculosis among
R. Steffen et al. / International Journal of Antimicrobial Agents 21 (2003) 175 /180
air travellers is estimated to be 5 /100/100 000 passengers, depending on the route of the plane. Nevertheless, transmission in flight or during prolonged train and bus rides have only rarely been reported and outdoor transmission might be ignored unless there is repeated exposure, as it may occur particularly among long-term, low-budget travellers or expatriates [24]. The risk of cholera is approximately 0.2/100 000, although asymptomatic and oligosymptomatic infections may be more frequent, as demonstrated in Japanese travellers [25,26]. The case fatality rate is less than 2% among travellers. For several potentially vaccine preventable diseases the risk of infection is less than 1 per million. Although a few dozen cases of Japanese encephalitis have been diagnosed in civilian travellers within the last 25 years, the attack rate in civilians is less than 1 per million because of the number of travellers. Exceptionally a short-term tourist in Bali was affected [27]. Only two international travellers have been diagnosed with plague since 1966. Very few anecdotal reports have documented tick borne encephalitis in international travellers, although the disease occurs in persons hiking or camping in endemic areas. So far no data have been published on the risk of influenza in this population, but various outbreaks on cruise ships or after a flight have been described.
5. Conclusions From the epidemiological basis described above, it is clear that future travellers should receive: All required immunizations. If health professionals do not comply with this rule, serious problems may arise as a traveller may be refused entry to the country, or he may be quarantined or immunized at the airport upon arrival. Often a fine has to be paid. All routine immunizations, based on the various national programmes. The appropriate recommended immunizations. The art of travel medicine is not to give all available vaccines */this would result in unnecessary costs and adverse events / /but to make the correct arbitrary decision how far down the priority list (Table 1) he should recommend protection. It is certainly wrong to protect a traveller against rare and less serious infections, while leaving him or her at risk of those more frequent and more serious. As shown in Table 2, the expert authorities in most countries and at WHO have a similar rating related to travel vaccines, the crucial matter is to detect pre-travel who belongs to the ‘risk groups’. Table 3 describes the characteristics to be considered. One should, however, not only consider environmental and travel characteristics as host factors may also
179
play a role. For instance it is useless to immunize persons against hepatitis A who already have acquired lifelong immunity by infection. This is often the case in those from the lower socio-economic strata of developing countries or after the history of jaundice, or in persons who have been born before World War II anywhere in the world.
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