Epidemiology and Outbreaks of Interest—From ISTM
Conference Coverage
By Lin H. Chen, MD
A number of epidemiology and outbreak reports were also presented at the 7th Conference of the International Society of Travel Medicine in May 2001. A plenary session titled Under-Appreciated Infectious Risks in Travel Medicine included discussions on tuberculosis (TB).
Cobelens F, Van Deutekom H. Tuberculosis. CISTM7. PL03.03.
The epidemiology of TB was reviewed by Dr. Frank Cobelens. One third of the world’s population has been infected with TB. Approximately 8.4 million infections occur per year, and 2 million deaths occur each year. WHO studies of TB in 54 settings showed that up to 37% are resistant to at least 1 drug, 0-14% are multidrug-resistant (MDR) TB. In some of the settings studied in Russia, Iran, China, and Estonia, 75% of cases were shown to be MDR TB. The risk of TB in long-term travelers to areas of high incidence has been estimated to be 3/1000 per month. Therefore, the risk of latent TB infection (LTBI) in travelers is greater than hepatitis B, typhoid fever, or meningococcal disease.
The 2 approaches to prevention of TB in travelers are: 1) vaccination with BCG; and 2) identification of LTBI using a tuberculin skin test (TST) followed by prophylactic treatment. The protective efficacy of BCG against TB has been difficult to predict for the individual traveler. The duration of BCG protection is unclear (?10-15 years), and there is limited data on the efficacy of repeated BCG vaccinations. TST, on the other hand, is dependent upon good technique, proper interpretation, and the tuberculin used. The sensitivity of TST is decreased in individuals with cellular immune suppression. The specificity of TST may be complicated by the booster effect, which may result from LTBI in individuals with waning immunity, as well as atypical mycobacterial infections and past BCG vaccinations. In order to reconcile the effect of BCG on TST, 2-step testing at a 1-week interval is recommended in travelers who have had BCG vaccination in the remote past, looking for a booster response.
For the travel medicine consultants who treat patients diagnosed with LTBI, there is an increasing choice of regimens. Isoniazid for 6-9 months is the most common therapy currently but is associated with hepatotoxicity in 1% of patients. If resistance were suspected, the combination of rifampin and pyrazinamide for 2 months becomes the regimen of choice. If intolerance to pyrazinamide were to develop, rifampin alone would be used for 4 months. Patients need to be monitored clinically for hepatotoxicity and baseline liver function tests considered in patients with increased risk for hepatotoxicity.
Metteeli A, et al. Tuberculosis in travelers and long-term immigrants. CISTM7. FC05.05.
GeoSentinel, a global surveillance network of travel and tropical medicine clinics established to track disease trends in travelers, has been collecting data on confirmed TB cases in travelers (T), long-term immigrants (LTI), and short-term immigrants (STI). LTI are those who immigrated 5 or more years prior to the diagnosis. The network has registered 10,785 T/LTI, and 2786 STI from January 1997 through November 2000. There were 95 TB cases among the STI (rate = 3.41%) and 44 TB cases among T/LTI (rate = 0.45%). Seven of these cases occurred in travelers/expatriates. This information should lead to some clarification of TB risk in travelers.
Cartwright K. Meningococcal disease and its prevention in travelers. CISTM7. PL03.01.
In the plenary session on Under-Appreciated Infectious Risks in Travel Medicine, Dr. Keith Cartwright highlighted the epidemiology of meningococcal disease. In the "meningitis belt," strains of serogroup A account for 80-90% of disease, while serogroup C strains cause 10-20% of disease. Peak attack rates reach 500/105 inhabitants in dry season, and epidemics occur every 5-10 years. Bivalent (A,C) and quadrivalent (A, C, Y, W-135) vaccines are available. Serogroup W-135 outbreaks occurred in 1999 and 2000 and were traced to pilgrims, the Haj, and their contacts. This session underscored the importance of immunizing pilgrims going to the Haj with the quadrivalent vaccine. Travelers planning longer stays in countries with high incidence of meningococcal disease (meningitis belt of Africa) should also receive the vaccine. Cases of meningococcal W135 disease related to Haj pilgrimage have also been reported in 2001. As a result, Saudi Arabia will be requiring the quadrivalent meningococcal vaccine for pilgrims going to the Haj (Promed V2001 #146, June 24).
Pepin J. African trypanosomiasis: Current epidemiology, clinical characteristics and diagnosis. CISTM7. SY04.03; Jelinek T, et al. Tropneteurop: Outbreak of African trypanosomiasis among travelers to the Serengeti National Park in Tanzania. CISTM7. FC05.06.
African trypanosomiasis is a protozoal infection spread by the tsetse fly. The incidence of T brucei gambiense has increased because of civil unrest in endemic areas, such as Republic of the Congo, Angola, Sudan, and Uganda. Gambian trypanosomiasis is not a significant concern in travelers but is a problem with migrants. The incidence of T brucei rhodesiense remains low. However, TropNetEurop has reported a number of cases in travelers to the game parks of East Africa since February 2001. These reports demonstrate the importance of increased awareness through global networks. Travel medicine specialists should consider African trypanosomiasis in travelers returning from East Africa with fevers and skin lesions, which are typically chancres. Additional cases of Rhodesian trypanosomiasis have been reported since the conference—2 contracted in Tarangire National Park in Tanzania and 1 in Serengeti (Promed V2001 #143, June 19, and V2001 #146, June 24).
Bauer I. Knowledge and behaviour of tourists to Manu National Park/Peru in relation to leishmaniasis. CISTM7. FC01.05.
Lack of knowledge regarding leishmaniasis was demonstrated by a study on tourists going to Manu National Park in Peru. Similar to a CDC report on leishmaniasis in travelers to Costa Rica last year, few tourists knew of leishmaniasis (6%). Among the tourists given a handout with information on leishmaniasis, one third paid more attention to personal protective measures as a result of the information from the handout.
Bodnar U, et al. Descriptive epidemiology of influenza among cruise ship travelers to the Alaska region, 1999-2000. CISTM7. FC05.03.
Following the 1998 summertime outbreak of influenza A in travelers to Alaska and the Yukon Territory, surveillance of acute respiratory illnesses (ARI), and influenza-like illness (ILI) among cruise ship travelers to the Alaska region was conducted and described for 1999 and 2000. In 1999, a summertime influenza A epidemic was identified, including 5330 cases of ARI and 2357 cases of ILI among passengers and crew of cruise ships. In 2000, no influenza epidemic was identified, with 1511 cases of ARI and 385 cases of ILI (preliminary data from CDC). Most passengers with ARI were older than 60 years and have increased risk for complications from influenza. Therefore, vaccination against influenza should be recommended for high-risk travelers who are not vaccinated during the previous fall or winter before their participation in large organized tour groups.
Xu HM, et al. Malaria distribution in the People’s Republic of China. CISTM7. PO01.08.
Data on malaria incidence were obtained from the Chinese Ministry of Public Health in 1999. A total of 29,039 cases were reported, resulting in 67 deaths. A total of 5466 cases and 227 carriers of P falciparum were identified. However, the actual number of malaria cases was estimated to be 250,000-300,000 in 1999. Malaria affects primarily Hainan and Yunnan provinces. The risk of malaria is felt to be very low for most travelers to China, and prophylaxis is not usually recommended. However, malaria may be a risk in parts of Yunnan and Hainan, and travel medicine consultants should consider malaria chemoprophylaxis for travelers going to these areas.
Reimer B, et al. Prevalence and incidence of Lyme borreliosis in south and east Bavaria, Germany. CISTM7. PO08.14.
A seroprevalence study on Borrelia burgdorferi, sensu lato, was done in South Bavaria, Germany. Of the 4758 subjects examined, 14% showed IgG and/or IgM antibodies at the start of the study. These subjects were all asymptomatic for Lyme disease. About 77% of the seropositive subjects randomly selected to have immunoblot showed Borrelia-specific bands. After 1 and 2 years, serological testing was again performed and showed 35 subjects had seroconverted to positive (seroconversion rate = 5 per 1000 person-observation years). A total of 27 of these 35 seroconverters were asymptomatic, while 8 of 35 had erythema migrans (EM) during the study period. There were 37 additional clinical cases of EM without detectable antibodies, attributed to treatment with antibiotics. The incidence of Borrelia infection in this population was 1.1% per year. Although the incidence is relatively low, travelers with high-risk activities such as hiking and camping should be advised regarding the presence of Lyme disease in Bavaria.
Kaiser R. Tick-borne encephalitis in Germany and clinical course of the disease. CISTM7. ST07.05; Suss J, Schrader C. Epidemiological consideration of TBE. CISTM7. ST08.01; Haglund M. TBE: Diagnosis, clinical features and long-term sequelae. CISTM7. ST08.02; Kunze M. TBE: A global traveling issue. CISTM7. ST08.03; Eder G. TBE: Virology and active immunization. CISTM7. ST08.04.
A satellite symposium was held on tick-borne encephalitis (TBE). This disease is endemic in Austria, where the conference was held, as well as Germany, Czech Republic, Poland, Slovenia, Russia, Latvia, Lithuania, Estonia, Sweden, and Finland. It is felt that the increasing tourism to endemic countries and increasing movement of people will lead to more TBE infections. More than 10,000 hospitalized TBE cases are registered annually, but the incidence is felt to be underestimated in travelers, as many countries do not screen for TBE regularly.
TBE is caused by a virus in the family Flaviviridae, and carried by ixodid ticks. The disease commonly presents as meningitis or meningoencephalitis, and less commonly as encephalomyelitis. The patients complain of severe headaches, fever, vomiting, and ataxia. Patients with meningoencephalitis and elderly patients have a more serious course of illness, often with somnolence and coma. Many patients have long-term sequelae such as paresis, impaired coordination, and neuropsychiatric and cognitive dysfunction. Diagnosis of TBE is made by detection of TBE-specific IgM and IgG antibodies in serum. Treatment is supportive. Although an efficacious vaccine is available in Europe, it is not available in the United States. Travel Medicine consultants should advise high-risk travelers (those planning outdoor activities like hiking and camping) of TBE, and these consultants should consider the diagnosis in returning travelers with signs and symptoms consistent with TBE.
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