Regional Variation in Travel-Related Illness in Africa
Regional Variation in Travel-Related Illness in Africa
Our study provides an evidence base of regional infectious disease exposures among travelers returning from Africa. These data show a profile of travel-related illness that differs with that of resident populations in these regions; this knowledge is essential in prioritizing preventive measures for the approximately 50 million travelers to Africa each year. Diarrheal and other gastrointestinal illnesses, hepatitis A, dog bites, and a very low proportion of febrile illnesses characterized the health of travelers returning from Northern Africa. In contrast, febrile illnesses were the predominant cause of clinic visits in travelers returning from sub-Saharan Africa, although considerable differences were evident in the etiology of fever in travelers from different regions. Malaria, which was most common in travelers returning from Central and Western Africa, was seen infrequently in travelers to Southern and Northern Africa. The incidence of helminthic infections also varied considerably: schistosomiasis and strongyloidiasis predominated in travelers returning from Eastern and Western Africa, but 82 of 86 L. loa infections reported in this study were diagnosed in travelers returning from Central Africa (Table 4). HIV infection and tuberculosis dominate the incidence of disease for much of sub-Saharan Africa and are an increasing concern for travelers, but our results show that these infections were rarely diagnosed in travelers at GeoSentinel Sites (Table 4).
Several factors likely contributed to our observations. Certain illnesses related to travel in Africa are more common in particular demographic groups. For instance, malaria is more common in travelers VFR than in tourists. In our study, malaria-related deaths occurred most often in men who traveled for business, a finding that may have implications for companies with expanding business interests in Africa. Pretravel medical advice and use of effective malaria prevention measures and chemoprophylaxis are essential for business travelers to areas of risk. Quantifying malaria risk is difficult, but the regional profiles presented here in which malaria predominated as a diagnosis are useful indicators (Table 3, Table 5). High rates of malaria in Western and Central Africa reflect high malaria transmission levels in these areas. Entomologic inoculation rates (the number of infectious mosquito bites that a person receives in a certain time period) are a useful indicator of malaria risk. For example, the entomological inoculation rate for Bayma in Sierra Leone (Nov 1990–Oct 1991) was 884, compared with 1.5 for Kilifi Town in Kenya during the same period.
For some infections, such as the helminthic infections loaisis and onchocerciasis, vector distribution affects acquisition. Seasonal and climatic factors and degree of endemicity influence the likelihood of malaria and dengue transmission, whereas food and water hygiene, along with differences in sanitation, influence acquisition of diarrheal diseases. Illnesses that are commonly self-limiting and often have mild symptoms, such as influenza and dengue, are less likely to result in a visit to a clinic. Furthermore, travelers in a sub-Saharan Africa country who have fever may be examined by clinicians who will treat them empirically for malaria and thus misdiagnose another infection.
The finding that travelers were rarely seen in GeoSentinel site clinics for VPI, irrespective of the region visited, extends previous observations from Southern Africa and remains a paradox, considering that rates of vaccination against these illnesses are historically <45%. We hypothesize that subclinical infection of children with hepatitis A or the low likelihood of adults or children with mild influenza-like illness to seek medical attention may account for low numbers of these 2 VPI reported from GeoSentinel sites. Most hepatitis A cases were in travelers to Northern Africa, which reflects the high rate of gastrointestinal infections from that region (Table 3). Our findings emphasize the importance of hepatitis A vaccination, which should be emphasized to health care providers and travelers alike, particularly when Northern Africa is the intended travel destination.
The high number of animal bites and the subsequent need for rabies PEP in travelers returning from Northern Africa are likely to reflect bias because 97% of GeoSentinel-reported cases in travelers returning from Northern Africa who sought rabies PEP were reported to the Marseille, France, site, which is a reference center for management of suspected rabies exposures. However, the paucity of reported bites and need for rabies PEP at GeoSentinel sites among travelers returning from sub-Saharan Africa may in part reflect that travelers to sub-Saharan Africa were more often travelers VFR or long-term travelers, who may be more likely than tourists to Northern Africa to seek treatment at the time of exposure.
Sixty-seven percent of the world's HIV-infected population resides in sub-Saharan Africa, and tuberculosis prevalence in some regions of Africa approaches 1%. Because 5%–50% of travelers report casual sexual experiences while traveling, it is surprising that so few cases of acute HIV infection were documented in travelers examined in GeoSentinel sites if risk behavior and endemicity of infection are high in many regions. Travelers who have symptoms of HIV and other sexually transmitted infections may seek care at specialty clinics rather than at GeoSentinel sites. However, because symptoms of acute HIV infection are commonly protean, and often manifest as a nonspecific febrile illness, travelers are as likely to go to GeoSentinel clinic sites as to specialist clinics. HIV should always be considered as a differential diagnosis in febrile returning travelers or in travelers who have clinical features compatible with HIV seroconversion illness. Regarding tuberculosis, although reactivation of latent infection may occur many years after acquisition, it is noteworthy that despite the large number of tuberculosis cases in most regions of sub-Saharan Africa, so few symptomatic cases occurred in travelers to Africa during the prolonged period of this study.
Previous studies of illnesses acquired by travelers to Africa have focused on illnesses acquired from sub-Saharan Africa as a whole, have been conducted at a single center, or have had analyses limited to a single disease or infection. Strengths of the current study are data capture from 54 international surveillance sites and >500 different diagnoses, enabling us to show regional patterns of illness in Africa. In addition, data were collected during an extended time period, which may offset acute spikes in reporting particular diagnoses that could skew the data.
Discussion
Our study provides an evidence base of regional infectious disease exposures among travelers returning from Africa. These data show a profile of travel-related illness that differs with that of resident populations in these regions; this knowledge is essential in prioritizing preventive measures for the approximately 50 million travelers to Africa each year. Diarrheal and other gastrointestinal illnesses, hepatitis A, dog bites, and a very low proportion of febrile illnesses characterized the health of travelers returning from Northern Africa. In contrast, febrile illnesses were the predominant cause of clinic visits in travelers returning from sub-Saharan Africa, although considerable differences were evident in the etiology of fever in travelers from different regions. Malaria, which was most common in travelers returning from Central and Western Africa, was seen infrequently in travelers to Southern and Northern Africa. The incidence of helminthic infections also varied considerably: schistosomiasis and strongyloidiasis predominated in travelers returning from Eastern and Western Africa, but 82 of 86 L. loa infections reported in this study were diagnosed in travelers returning from Central Africa (Table 4). HIV infection and tuberculosis dominate the incidence of disease for much of sub-Saharan Africa and are an increasing concern for travelers, but our results show that these infections were rarely diagnosed in travelers at GeoSentinel Sites (Table 4).
Several factors likely contributed to our observations. Certain illnesses related to travel in Africa are more common in particular demographic groups. For instance, malaria is more common in travelers VFR than in tourists. In our study, malaria-related deaths occurred most often in men who traveled for business, a finding that may have implications for companies with expanding business interests in Africa. Pretravel medical advice and use of effective malaria prevention measures and chemoprophylaxis are essential for business travelers to areas of risk. Quantifying malaria risk is difficult, but the regional profiles presented here in which malaria predominated as a diagnosis are useful indicators (Table 3, Table 5). High rates of malaria in Western and Central Africa reflect high malaria transmission levels in these areas. Entomologic inoculation rates (the number of infectious mosquito bites that a person receives in a certain time period) are a useful indicator of malaria risk. For example, the entomological inoculation rate for Bayma in Sierra Leone (Nov 1990–Oct 1991) was 884, compared with 1.5 for Kilifi Town in Kenya during the same period.
For some infections, such as the helminthic infections loaisis and onchocerciasis, vector distribution affects acquisition. Seasonal and climatic factors and degree of endemicity influence the likelihood of malaria and dengue transmission, whereas food and water hygiene, along with differences in sanitation, influence acquisition of diarrheal diseases. Illnesses that are commonly self-limiting and often have mild symptoms, such as influenza and dengue, are less likely to result in a visit to a clinic. Furthermore, travelers in a sub-Saharan Africa country who have fever may be examined by clinicians who will treat them empirically for malaria and thus misdiagnose another infection.
The finding that travelers were rarely seen in GeoSentinel site clinics for VPI, irrespective of the region visited, extends previous observations from Southern Africa and remains a paradox, considering that rates of vaccination against these illnesses are historically <45%. We hypothesize that subclinical infection of children with hepatitis A or the low likelihood of adults or children with mild influenza-like illness to seek medical attention may account for low numbers of these 2 VPI reported from GeoSentinel sites. Most hepatitis A cases were in travelers to Northern Africa, which reflects the high rate of gastrointestinal infections from that region (Table 3). Our findings emphasize the importance of hepatitis A vaccination, which should be emphasized to health care providers and travelers alike, particularly when Northern Africa is the intended travel destination.
The high number of animal bites and the subsequent need for rabies PEP in travelers returning from Northern Africa are likely to reflect bias because 97% of GeoSentinel-reported cases in travelers returning from Northern Africa who sought rabies PEP were reported to the Marseille, France, site, which is a reference center for management of suspected rabies exposures. However, the paucity of reported bites and need for rabies PEP at GeoSentinel sites among travelers returning from sub-Saharan Africa may in part reflect that travelers to sub-Saharan Africa were more often travelers VFR or long-term travelers, who may be more likely than tourists to Northern Africa to seek treatment at the time of exposure.
Sixty-seven percent of the world's HIV-infected population resides in sub-Saharan Africa, and tuberculosis prevalence in some regions of Africa approaches 1%. Because 5%–50% of travelers report casual sexual experiences while traveling, it is surprising that so few cases of acute HIV infection were documented in travelers examined in GeoSentinel sites if risk behavior and endemicity of infection are high in many regions. Travelers who have symptoms of HIV and other sexually transmitted infections may seek care at specialty clinics rather than at GeoSentinel sites. However, because symptoms of acute HIV infection are commonly protean, and often manifest as a nonspecific febrile illness, travelers are as likely to go to GeoSentinel clinic sites as to specialist clinics. HIV should always be considered as a differential diagnosis in febrile returning travelers or in travelers who have clinical features compatible with HIV seroconversion illness. Regarding tuberculosis, although reactivation of latent infection may occur many years after acquisition, it is noteworthy that despite the large number of tuberculosis cases in most regions of sub-Saharan Africa, so few symptomatic cases occurred in travelers to Africa during the prolonged period of this study.
Previous studies of illnesses acquired by travelers to Africa have focused on illnesses acquired from sub-Saharan Africa as a whole, have been conducted at a single center, or have had analyses limited to a single disease or infection. Strengths of the current study are data capture from 54 international surveillance sites and >500 different diagnoses, enabling us to show regional patterns of illness in Africa. In addition, data were collected during an extended time period, which may offset acute spikes in reporting particular diagnoses that could skew the data.
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