Abstract

Background

With the popularity of international travel increasing, more travelers in endemic areas may increase their risk of tuberculosis (TB). We analyzed Peace Corps data to assess the risk of TB in long‐term travelers from the United States.

Methods

We analyzed purified protein derivative (PPD) conversion and acute TB case data from the Peace Corps Epidemiological Surveillance System as well as postservice claims data. We calculated the risk of PPD conversion and active TB in all countries with Peace Corps Volunteers between 1996 and 2005 and compared these risks with other published data.

Results

The overall incidence rates for positive PPD conversions and active TB cases are 1.283 and 0.057 per 1,000 Volunteer‐months, respectively. The Africa region had the highest PPD conversion rate of 1.467 conversions per 1,000 Volunteer‐months as well as the highest active TB rate of 0.089 cases per 1,000 Volunteer‐months. Per‐country incidence rates for PPD conversions and active TB cases ranged widely from 0.000 to 5.514 cases and 0.000 to 2.126 cases per 1,000 Volunteer‐months, respectively. In countries identified as “high risk,” there were 1.436 cases of PPD conversions and 0.084 cases of active TB per 1,000 Volunteer‐months.

Conclusions

Peace Corps Volunteers have significantly higher rates of TB when compared to the average US population but much lower than those reported for travelers to highly endemic countries. Volunteers assigned to highly endemic countries still have a lower risk compared to other travelers to those same countries. Keeping in mind that Peace Corps Volunteers are a unique population, these data may be useful in providing medical advice to long‐term travelers.

Recent media reports related to extensively drug‐resistant tuberculosis (TB) have renewed concerns about this pernicious disease.1 TB remains one of the most prevalent diseases in the world, with an estimated 14.6 million cases worldwide and nearly 1.7 million deaths from TB in 2004.2 The United States has had some success in reducing TB cases each year since 1993 to a current incidence rate of 4.8 cases per 100,000 population in 2005.3 However, with the popularity of international travel increasing, especially to areas of high risk such as Africa, 4 more travelers in endemic areas may increase their risk of TB.

Published research has shown a substantial increase in TB risk among travelers to highly endemic areas. The most recent study showed a purified protein derivative (PPD) conversion rate of 2.8 cases per 1,000 person‐months of travel among Dutch travelers 5 as well as an active TB rate of 0.6 cases per 1,000 person‐months of travel. We found no recent systematic data specifically related to TB risk in US travelers.

US Peace Corps Volunteers spend 27 months living in countries often endemic for TB and are thus a unique population in which to assess risk. All Peace Corps Volunteers are screened with a PPD test prior to service and receive a PPD test at midservice and upon completion of service. Clinical testing for active TB, as well as screening PPD tests, is also provided at any time during service when exposure may have occurred. Peace Corps also provides a postservice claims system for reimbursement of treatment costs for service‐related illnesses, including both latent and active TB.

Since President John F. Kennedy established the Peace Corps on March 1, 1961, more than 187,000 Peace Corps Volunteers have been invited by 139 host countries to work on issues including education, business development, and health.6

To quantify TB risk for long‐term travelers from the United States, we analyzed Peace Corps epidemiological surveillance data to assess the risk of TB in countries where Volunteers served from 1996 to 2005.

Methods

We analyzed data from the Peace Corps Epidemiological Surveillance System, 7 which collects monthly counts of specific conditions among currently serving Peace Corps Volunteers from Peace Corps Medical Officers stationed in each Peace Corps country. Since January 1, 1996, these reports have included counts of PPD test conversions (defined as an increase in induration from the baseline test using criteria from the US Centers for Disease Control and Prevention 8 ), as well as cases of active TB (defined as an infection with Mycobacterium tuberculosis confirmed by culture of the organism from a collected clinical specimen or a clinical presentation consistent with active TB that is culture negative but responds to treatment with appropriate anti‐TB therapy). Peace Corps surveillance data does not include protected health information or identifying personal or demographic information, and it does not distinguish between diagnoses made clinically or microbiologically, pulmonary or extrapulmonary cases, smear positive or negative, or culture positive or negative.

Some Volunteers may have had PPD conversions or active TB prior to their Peace Corps service. In each case, the reading of subsequent PPD tests is interpreted accordingly based on guidelines of the US Centers for Disease Control and Prevention for placing and reading PPD tests. All Peace Corps Medical Officers are trained to follow these guidelines. Therefore, PPD conversions reported via the Peace Corps surveillance system do take a Volunteer’s PPD history into account.

In addition to the cases reported during in‐service medical care, Peace Corps Volunteers are provided testing and evaluation immediately upon completion of service; occasionally, Volunteers receive their examinations subsequent to completion of service due to logistical reasons. The completion rate of postservice PPD testing exceeds 99%. If a Volunteer is determined to have a PPD conversion or active TB at this point, he or she can file a claim for treatment costs via the Federal Employees’ Compensation Act. We counted all those claims filed for positive PPD test conversions (ICD‐9 code 795.5) and active TB (ICD‐9 codes 010–018) for Volunteers who closed service between January 1, 1996, and December 31, 2005.

We calculated the total number of PPD conversions and active TB cases for each Peace Corps country that hosted Volunteers between January 1, 1996, and December 31, 2005. Claims filed after completion of service were counted in the year that the Volunteer completed service.

To calculate incidence rates, we obtained the number of Volunteer‐years for each country that hosted Peace Corps Volunteers at any time between January 1, 1996, and December 31, 2005. For consistency with published reports on TB risk among travelers, we reported results based on Volunteer‐months, which were calculated by multiplying Volunteer‐years by 12.

We calculated incidence rates in seven geographic regions: Europe and Central Asia (Europe), East and South Asia (Asia), Africa, Central America, Caribbean, South America, and the Pacific Islands. For administrative reasons, some Peace Corps posts (ie, Malta, Niue, and Tuvalu) reported cases with another country (Tunisia, Samoa, and Fiji, respectively) and are counted and reported as single‐country units. Posts in the Leeward Islands, Windward Islands, and St Kitts and Nevis are combined collectively as “Eastern Caribbean,” and data from these posts include Volunteers on Antigua, Barbuda, Dominica, Grenada, Cariaccou, St Lucia, St Vincent, and the Grenadines. The Peace Corps operated two separate posts in Russia (Western and Far East), and counts from these locations were calculated separately and are also placed in two distinct geographic regions (Europe and Asia, respectively). Peace Corps posts in Comoros, Cook Islands, and Seychelles each closed in January 1996 and thus did not contribute to the counts or Volunteer‐years in this study.

The World Health Organization 9 and Corbett and colleagues 10 have identified high‐risk countries with respect to TB. We examined the TB rates of Volunteers in 19 of these countries where Peace Corps placed Volunteers between 1996 and 2005.

Results

Over the 10‐year study period, there were 44,070 Volunteers who contributed 801,780.54 Volunteer‐months of service. The mean age at the start of service was 28.1 years (median 24.4 y, range 18–84 y), with 59.3% female and 16% self‐identified as an ethnic minority. Among these Volunteers, there were a total of 1,028 PPD conversions and 46 active cases of TB. The overall incidence rates for PPD conversions and active TB cases are 1.283 and 0.057 per 1,000 Volunteer‐months, respectively.

There were 1,282 Volunteers (2.9%) who had a history of a positive PPD conversion or active TB disease prior to beginning Peace Corps service. These 1,282 Volunteers contributed 20,116.08 months (2.5%) of service during our study period. We were unable to distinguish how many had either a PPD conversion or an active disease prior to service, nor were we able to obtain specific counts of PPD conversion or active disease during service among those with a prior history.

Tables 1 to 7 show all countries with Peace Corps Volunteers between January 1, 1996, and December 31, 2005, by geographic regions, the calendar years and the total number of months in which they hosted Volunteers, the total number of Volunteer‐years for each country, the total number of PPD conversions and active cases of TB reported for each country within the indicated time period, and the incidence rate per 1,000 Volunteer‐months. The total number of months that Volunteers served in each country correlates with the number of monthly surveillance reports that were obtained from each country.

Table 1

Peace Corps countries—Europe and Central Asia

Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Albania 1996–2005 42 208.424 2.799 0.000 
Armenia 1996–2005 117 674.626 19 2.347 0.000 
Azerbaijan 2003–2005 27 113.103 0.737 0.000 
Bulgaria 1996–2005 119 1,212.449 23 1.581 0.000 
Czech Republic 1996–1997 17 72.731 0.000 0.000 
Estonia 1996–2002 75 230.530 1.084 0.000 
Georgia 2001–2005 56 208.329 0.400 0.000 
Hungary 1996–1997 90.680 5.514 0.000 
Jordan 1997–2005 90 393.350 0.636 0.000 
Kazakhstan 1996–2005 120 1,133.749 33 2.426 0.147 
Kyrgyzstan 1996–2005 115 746.023 15 1.676 0.112 
Latvia 1996–2002 78 264.025 0.947 0.000 
Lithuania 1996–2002 79 292.756 1.423 0.000 
Macedonia 1998–2005 70 257.823 1.293 0.000 
Moldova 1996–2005 120 943.721 17 1.501 0.000 
Mongolia 1996–2005 119 738.650 10 1.128 0.000 
Poland 1996–2001 66 742.256 0.561 0.112 
Romania 1996–2005 119 1,337.673 10 0.623 0.000 
Russia Western 1996–2003 85 538.321 17 2.632 0.000 
Slovakia 1996–2002 79 512.235 1.139 0.000 
Turkmenistan 1996–2005 114 619.556 18 2.421 0.135 
Ukraine 1996–2005 120 2,057.117 28 1.134 0.000 
Uzbekistan 1996–2005 106 882.207 12 1.134 0.094 
Total — — 14,270.334 247 1.442 0.035 
Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Albania 1996–2005 42 208.424 2.799 0.000 
Armenia 1996–2005 117 674.626 19 2.347 0.000 
Azerbaijan 2003–2005 27 113.103 0.737 0.000 
Bulgaria 1996–2005 119 1,212.449 23 1.581 0.000 
Czech Republic 1996–1997 17 72.731 0.000 0.000 
Estonia 1996–2002 75 230.530 1.084 0.000 
Georgia 2001–2005 56 208.329 0.400 0.000 
Hungary 1996–1997 90.680 5.514 0.000 
Jordan 1997–2005 90 393.350 0.636 0.000 
Kazakhstan 1996–2005 120 1,133.749 33 2.426 0.147 
Kyrgyzstan 1996–2005 115 746.023 15 1.676 0.112 
Latvia 1996–2002 78 264.025 0.947 0.000 
Lithuania 1996–2002 79 292.756 1.423 0.000 
Macedonia 1998–2005 70 257.823 1.293 0.000 
Moldova 1996–2005 120 943.721 17 1.501 0.000 
Mongolia 1996–2005 119 738.650 10 1.128 0.000 
Poland 1996–2001 66 742.256 0.561 0.112 
Romania 1996–2005 119 1,337.673 10 0.623 0.000 
Russia Western 1996–2003 85 538.321 17 2.632 0.000 
Slovakia 1996–2002 79 512.235 1.139 0.000 
Turkmenistan 1996–2005 114 619.556 18 2.421 0.135 
Ukraine 1996–2005 120 2,057.117 28 1.134 0.000 
Uzbekistan 1996–2005 106 882.207 12 1.134 0.094 
Total — — 14,270.334 247 1.442 0.035 

PPD = purified protein derivative; TB = tuberculosis.

Table 2

Peace Corps countries—East Asia and South Asia

Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Bangladesh 1998–2005 77 323.439 0.773 0.000 
China 1996–2005 106 478.283 16 2.788 0.174 
East Timor 2002–2005 43 92.923 0.897 0.000 
Nepal 1996–2004 104 1,091.636 24 1.832 0.000 
Philippines 1996–2005 120 1,216.559 0.411 0.000 
Russia Far East 1996–2003 84 388.569 1.501 0.000 
Sri Lanka 1996–1998, 2005 34 72.621 0.000 0.000 
Thailand 1996–2005 120 733.574 15 1.704 0.000 
Total — — 4,397.604 72 1.364 0.019 
Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Bangladesh 1998–2005 77 323.439 0.773 0.000 
China 1996–2005 106 478.283 16 2.788 0.174 
East Timor 2002–2005 43 92.923 0.897 0.000 
Nepal 1996–2004 104 1,091.636 24 1.832 0.000 
Philippines 1996–2005 120 1,216.559 0.411 0.000 
Russia Far East 1996–2003 84 388.569 1.501 0.000 
Sri Lanka 1996–1998, 2005 34 72.621 0.000 0.000 
Thailand 1996–2005 120 733.574 15 1.704 0.000 
Total — — 4,397.604 72 1.364 0.019 

PPD = purified protein derivative; TB = tuberculosis.

Table 3

Peace Corps countries—Africa

Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Benin 1996–2005 119 1,018.828 0.654 0.000 
Botswana 1996–2005 58 228.657 1.093 0.364 
Burkina Faso 1996–2005 120 808.225 15 1.547 0.000 
Cameroon 1996–2005 119 1,315.513 49 3.104 0.380 
Cape Verde 1996–2005 120 449.840 0.741 0.000 
Central African Republic 1996 39.190 2.126 2.126 
Chad 1996–1998, 2003–2005 55 140.561 1.186 0.593 
Congo 1996–1997 13 64.255 1.297 0.000 
Cote d’Ivoire 1996–2002 81 764.635 29 3.161 0.109 
Eritrea 1996–1998 29 103.756 1.606 0.000 
Ethiopia 1996–1999 36 123.143 3.384 0.677 
Gabon 1996–2005 114 674.951 0.000 0.000 
Gambia 1996–2005 119 825.971 0.605 0.000 
Ghana 1996–2005 120 1,478.360 12 0.676 0.113 
Guinea 1996–2005 120 988.260 13 1.096 0.000 
Guinea‐Bissau 1996–1998 28 94.188 5.309 0.885 
Kenya 1996–2005 120 1,340.830 40 2.486 0.124 
Lesotho 1996–2005 119 863.461 21 2.027 0.290 
Madagascar 1996–2005 114 811.025 16 1.644 0.103 
Malawi 1996–2005 120 1,094.935 23 1.750 0.152 
Mali 1996–2005 119 1,580.000 59 3.112 0.053 
Mauritania 1996–2005 120 647.833 0.900 0.000 
Morocco 1996–2005 115 1,282.116 18 1.170 0.065 
Mozambique 1998–2005 87 380.624 0.876 0.000 
Namibia 1996–2005 119 1,022.160 14 1.141 0.082 
Niger 1996–2005 120 1,109.848 21 1.577 0.000 
Sao Tome 1996 9.810 0.000 0.000 
Senegal 1996–2005 120 1,325.692 11 0.691 0.000 
South Africa 1997–2005 107 763.770 0.655 0.000 
Swaziland 1996, 2003–2005 39 132.411 1.259 0.000 
Tanzania 1996–2005 120 1,100.860 11 0.833 0.076 
Togo 1996–2005 120 898.913 11 1.020 0.000 
Tunisia (Malta) 1996 21.676 0.000 0.000 
Uganda 1996–1999, 2001–2005 98 384.627 1.517 0.000 
Zambia 1996–2005 120 1,129.342 12 0.885 0.074 
Zimbabwe 1996–2001 71 371.652 1.570 0.000 
Total — — 25,389.918 446 1.464 27 0.089 
Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Benin 1996–2005 119 1,018.828 0.654 0.000 
Botswana 1996–2005 58 228.657 1.093 0.364 
Burkina Faso 1996–2005 120 808.225 15 1.547 0.000 
Cameroon 1996–2005 119 1,315.513 49 3.104 0.380 
Cape Verde 1996–2005 120 449.840 0.741 0.000 
Central African Republic 1996 39.190 2.126 2.126 
Chad 1996–1998, 2003–2005 55 140.561 1.186 0.593 
Congo 1996–1997 13 64.255 1.297 0.000 
Cote d’Ivoire 1996–2002 81 764.635 29 3.161 0.109 
Eritrea 1996–1998 29 103.756 1.606 0.000 
Ethiopia 1996–1999 36 123.143 3.384 0.677 
Gabon 1996–2005 114 674.951 0.000 0.000 
Gambia 1996–2005 119 825.971 0.605 0.000 
Ghana 1996–2005 120 1,478.360 12 0.676 0.113 
Guinea 1996–2005 120 988.260 13 1.096 0.000 
Guinea‐Bissau 1996–1998 28 94.188 5.309 0.885 
Kenya 1996–2005 120 1,340.830 40 2.486 0.124 
Lesotho 1996–2005 119 863.461 21 2.027 0.290 
Madagascar 1996–2005 114 811.025 16 1.644 0.103 
Malawi 1996–2005 120 1,094.935 23 1.750 0.152 
Mali 1996–2005 119 1,580.000 59 3.112 0.053 
Mauritania 1996–2005 120 647.833 0.900 0.000 
Morocco 1996–2005 115 1,282.116 18 1.170 0.065 
Mozambique 1998–2005 87 380.624 0.876 0.000 
Namibia 1996–2005 119 1,022.160 14 1.141 0.082 
Niger 1996–2005 120 1,109.848 21 1.577 0.000 
Sao Tome 1996 9.810 0.000 0.000 
Senegal 1996–2005 120 1,325.692 11 0.691 0.000 
South Africa 1997–2005 107 763.770 0.655 0.000 
Swaziland 1996, 2003–2005 39 132.411 1.259 0.000 
Tanzania 1996–2005 120 1,100.860 11 0.833 0.076 
Togo 1996–2005 120 898.913 11 1.020 0.000 
Tunisia (Malta) 1996 21.676 0.000 0.000 
Uganda 1996–1999, 2001–2005 98 384.627 1.517 0.000 
Zambia 1996–2005 120 1,129.342 12 0.885 0.074 
Zimbabwe 1996–2001 71 371.652 1.570 0.000 
Total — — 25,389.918 446 1.464 27 0.089 

PPD = purified protein derivative; TB = tuberculosis.

Table 4

Peace Corps countries—Central America

Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Belize 1996–2005 120 576.359 0.289 0.000 
Costa Rica 1996–2005 120 489.246 0.341 0.000 
El Salvador 1996–2005 120 1,078.850 14 1.081 0.077 
Guatemala 1996–2005 120 1,997.848 36 1.502 0.083 
Honduras 1996–2005 120 2,205.426 32 1.209 0.038 
Mexico 2004–2005 15 17.509 0.000 0.000 
Nicaragua 1996–2005 119 1,486.968 43 2.410 0.112 
Panama 1996–2005 120 1,059.652 0.550 0.079 
Total — — 8,911.858 136 1.272 0.065 
Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Belize 1996–2005 120 576.359 0.289 0.000 
Costa Rica 1996–2005 120 489.246 0.341 0.000 
El Salvador 1996–2005 120 1,078.850 14 1.081 0.077 
Guatemala 1996–2005 120 1,997.848 36 1.502 0.083 
Honduras 1996–2005 120 2,205.426 32 1.209 0.038 
Mexico 2004–2005 15 17.509 0.000 0.000 
Nicaragua 1996–2005 119 1,486.968 43 2.410 0.112 
Panama 1996–2005 120 1,059.652 0.550 0.079 
Total — — 8,911.858 136 1.272 0.065 

PPD = purified protein derivative; TB = tuberculosis.

Table 5

Peace Corps countries—Caribbean

Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Dominican Republic 1996–2005 120 1,560.879 28 1.495 0.000 
Eastern Caribbean 1998–2005 96 1,043.811 0.080 0.000 
Haiti 1996–2005 103 395.893 1.052 0.000 
Jamaica 1996–2005 120 1,024.572 14 1.139 0.081 
Total — — 4,025.155 48 0.994 0.021 
Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Dominican Republic 1996–2005 120 1,560.879 28 1.495 0.000 
Eastern Caribbean 1998–2005 96 1,043.811 0.080 0.000 
Haiti 1996–2005 103 395.893 1.052 0.000 
Jamaica 1996–2005 120 1,024.572 14 1.139 0.081 
Total — — 4,025.155 48 0.994 0.021 

PPD = purified protein derivative; TB = tuberculosis.

Table 6

Peace Corps countries—South America

Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Bolivia 1996–2005 120 1,554.401 17 0.911 0.000 
Chile 1996–1998 31 111.458 1.495 0.000 
Ecuador 1996–2005 120 1,619.600 21 1.081 0.051 
Guyana 1996–2005 119 414.842 13 2.611 0.000 
Paraguay 1996–2005 120 1,957.385 0.085 0.000 
Peru 2002–2005 41 225.541 0.000 0.000 
Suriname 1996–2005 120 365.175 0.228 0.000 
Uruguay 1996–1997 11 69.068 0.000 0.000 
Total — — 6,317.470 56 0.739 0.013 
Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Bolivia 1996–2005 120 1,554.401 17 0.911 0.000 
Chile 1996–1998 31 111.458 1.495 0.000 
Ecuador 1996–2005 120 1,619.600 21 1.081 0.051 
Guyana 1996–2005 119 414.842 13 2.611 0.000 
Paraguay 1996–2005 120 1,957.385 0.085 0.000 
Peru 2002–2005 41 225.541 0.000 0.000 
Suriname 1996–2005 120 365.175 0.228 0.000 
Uruguay 1996–1997 11 69.068 0.000 0.000 
Total — — 6,317.470 56 0.739 0.013 

PPD = purified protein derivative; TB = tuberculosis.

Table 7

Pacific Island Peace Corps countries

Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Fiji (Tuvalu) 1996–1997, 2003–2005 50 202.773 2.055 0.000 
Kiribati 1996–2005 118 438.905 0.380 0.190 
Marshall Island 1996 3.088 0.000 0.000 
Micronesia 1996–2005 119 567.003 0.147 0.000 
Papua New Guinea 1996–2001 66 388.249 0.215 0.000 
Samoa (Niue) 1996–2005 114 555.181 0.901 0.150 
Solomon Island 1996–2000 54 289.569 0.288 0.000 
Tonga 1996–2005 120 567.006 0.735 0.147 
Vanuatu 1996–2005 120 490.932 0.339 0.000 
Total — — 3,502.706 23 0.547 0.071 
Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Fiji (Tuvalu) 1996–1997, 2003–2005 50 202.773 2.055 0.000 
Kiribati 1996–2005 118 438.905 0.380 0.190 
Marshall Island 1996 3.088 0.000 0.000 
Micronesia 1996–2005 119 567.003 0.147 0.000 
Papua New Guinea 1996–2001 66 388.249 0.215 0.000 
Samoa (Niue) 1996–2005 114 555.181 0.901 0.150 
Solomon Island 1996–2000 54 289.569 0.288 0.000 
Tonga 1996–2005 120 567.006 0.735 0.147 
Vanuatu 1996–2005 120 490.932 0.339 0.000 
Total — — 3,502.706 23 0.547 0.071 

PPD = purified protein derivative; TB = tuberculosis.

The Africa region had the highest PPD conversion rate of 1.467 conversions per 1,000 Volunteer‐months, followed closely by the European region with 1.442. The Asia region had a PPD conversion rate of 1.364 per 1,000 Volunteer‐months, followed by Central America with 1.272, the Caribbean with 0.994, South America with 0.739, and the Pacific Islands with 0.547.

The Africa region also had the highest active TB rate of 0.089 cases per 1,000 Volunteer‐months, followed by the Pacific Islands with 0.071. Central America had an active TB case rate of 0.065 per 1,000 Volunteer‐years, followed by Europe with 0.039, the Caribbean with 0.021, the Asia region with 0.019, and South America with 0.013.

Per‐country incidence rates for PPD conversions and active TB cases ranged widely from 0.000 to 5.514 cases and 0.000 to 2.126 cases per 1,000 Volunteer‐months, respectively. Between 1996 and 2005, Peace Corps placed Volunteers in 19 countries identified as having high incidence rates of TB: Bangladesh, Botswana, China, Congo, Ethiopia, Haiti, Kenya, Lesotho, Malawi, Mozambique, Namibia, Philippines, Russia (Western and Far East), South Africa, Thailand, Uganda, Tanzania, Zambia, and Zimbabwe. Table 8 shows the data for these specific countries. In these countries, there were 1.436 cases of PPD conversions and 0.084 cases of active TB per 1,000 Volunteer‐months.

Table 8

Peace Corps Volunteers in high‐incidence countries

Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Bangladesh 1998–2005 77 323.439 0.773 0.000 
Botswana 1996–2005 58 228.657 1.093 0.364 
China 1996–2005 106 478.283 16 2.788 0.174 
Congo 1996–1997 13 64.255 1.297 0.000 
Ethiopia 1996–1999 36 123.143 3.384 0.677 
Haiti 1996–2005 103 395.893 1.052 0.000 
Kenya 1996–2005 120 1,340.830 40 2.486 0.124 
Lesotho 1996–2005 119 863.461 21 2.027 0.290 
Malawi 1996–2005 120 1,094.935 23 1.750 0.152 
Mozambique 1998–2005 87 380.624 0.876 0.000 
Namibia 1996–2005 119 1,022.160 14 1.141 0.082 
Philippines 1996–2005 120 1,216.559 0.411 0.000 
Russia Far East 1996–2003 84 388.569 1.501 0.000 
Russia Western 1996–2003 85 538.321 17 2.632 0.000 
South Africa 1997–2005 107 763.770 0.655 0.000 
Tanzania 1996–2005 120 1,100.860 11 0.833 0.076 
Thailand 1996–2005 120 733.574 15 1.704 0.000 
Uganda 1996–1999, 2001–2005 98 384.627 1.517 0.000 
Zambia 1996–2005 120 1,129.342 12 0.885 0.074 
Zimbabwe 1996–2001 71 371.652 1.570 0.000 
Total — — 12,942.954 223 1.436 13 0.084 
Peace Corps country Years as Peace Corps country Months with Volunteers, 1996–2005 Total Volunteer‐years Total PPD conversions PPD conversion rate per 1,000 Volunteer‐months Total active TB cases Active TB rate per 1,000 Volunteer‐months 
Bangladesh 1998–2005 77 323.439 0.773 0.000 
Botswana 1996–2005 58 228.657 1.093 0.364 
China 1996–2005 106 478.283 16 2.788 0.174 
Congo 1996–1997 13 64.255 1.297 0.000 
Ethiopia 1996–1999 36 123.143 3.384 0.677 
Haiti 1996–2005 103 395.893 1.052 0.000 
Kenya 1996–2005 120 1,340.830 40 2.486 0.124 
Lesotho 1996–2005 119 863.461 21 2.027 0.290 
Malawi 1996–2005 120 1,094.935 23 1.750 0.152 
Mozambique 1998–2005 87 380.624 0.876 0.000 
Namibia 1996–2005 119 1,022.160 14 1.141 0.082 
Philippines 1996–2005 120 1,216.559 0.411 0.000 
Russia Far East 1996–2003 84 388.569 1.501 0.000 
Russia Western 1996–2003 85 538.321 17 2.632 0.000 
South Africa 1997–2005 107 763.770 0.655 0.000 
Tanzania 1996–2005 120 1,100.860 11 0.833 0.076 
Thailand 1996–2005 120 733.574 15 1.704 0.000 
Uganda 1996–1999, 2001–2005 98 384.627 1.517 0.000 
Zambia 1996–2005 120 1,129.342 12 0.885 0.074 
Zimbabwe 1996–2001 71 371.652 1.570 0.000 
Total — — 12,942.954 223 1.436 13 0.084 

PPD = purified protein derivative; TB = tuberculosis.

Figure 1 shows the rate of PPD conversions and active TB among Peace Corps Volunteers per year for 1996 to 2005. Rates for PPD conversions ranged from 8.14 to 11.98 conversions per 1,000 Volunteers, and for active TB cases, from 0.00 to 0.93 cases per 1,000 Volunteers. Although the incidence rates appear to be trending downward over the 10‐year period (trendlines show β=−0.3134 and r2= 0.4643 for PPD conversions and β=−0.0746 and r2= 0.519 for active TB cases), a chi‐square test for trend found no significant difference in either PPD conversion or active TB rates.

Figure 1

TB rates among Peace Corps Volunteers, 1996 to 2005. TB = tuberculosis.

Figure 1

TB rates among Peace Corps Volunteers, 1996 to 2005. TB = tuberculosis.

Discussion

Our data show that Peace Corps Volunteers have significantly higher rates of TB when compared to the average US population (68.9 per 100,000 Volunteer‐years vs 4.8 per 100,000 person‐years in the US population). This is likely due to their exposure in countries with far higher rates of TB than the United States. Volunteer TB rates, however, are much lower than those reported for other travelers to highly endemic countries (1.3 per 1,000 Volunteer‐months vs 2.8 per 1,000 person‐months). Volunteers assigned to highly endemic countries still have a lower risk compared to general travelers (1.4 vs 2.8 PPD conversions and 0.08 vs 0.60 active TB cases per 1,000 person‐months).

One limitation of this study is that the Peace Corps Epidemiological Surveillance System does not count the number of Volunteers who have a particular condition but rather only the number of cases, so we are unable to provide the number or percentage of Volunteers who had PPD conversions or cases of active TB. However, given the nature of the disease, it is highly unlikely that a single Volunteer would be counted as having a PPD conversion or an active case of TB more than once during their service.

Peace Corps Volunteers serve in countries with varying levels of endemicity for TB. In addition, Peace Corps Volunteers are typically young and must be determined to be medically qualified for service. Also, Volunteers have good access to medical care during their service. These factors may affect the rate of TB infection and disease among Volunteers when compared to typical travelers to highly endemic countries.

Volunteers often live with host families, possibly presenting them with greater exposure to TB compared with the typical traveler. Additionally, most Volunteers spend a full 27 months in their host country, which is much longer than most travel itineraries, which average 23 days.11 This may explain the higher rate of TB among Volunteers compared to the US population.

There is a discrepancy between countries and regions in the ratio of PPD conversions to TB cases. For example, in the East/Southeast Asia region, there was only 1 TB case and 72 PPD conversions (ratio = 72), whereas in the Pacific Islands region, there were 3 TB cases for 23 PPD conversions (ratio = 7.7). This discrepancy may be explained by variations in the health status of Volunteers placed in various regions as well as variations in the types of placement locations available in each country.

Our data examine the risk over a 10‐year time period. In that time frame, although Volunteer medical services and policies with regard to TB have not changed significantly, Volunteer site placements, host country TB control measures, and Volunteer job assignments may have changed within each country. Thus, further analysis may be necessary to determine trends in TB risk among US travelers to these countries.

Our analysis presents PPD conversion data and active TB incidence for several countries based on a unique population of Peace Corps Volunteers. These data may prove useful for clinicians and travel advisors on the nature of the risk of TB for US travelers to other countries.

Acknowledgment

The authors acknowledge Dr David R. Hill for his thoughtful comments on their manuscript.

Declaration of interests

The authors state that they have no conflicts of interest.

References

1
Wines
M
.
Virulent TB in S. Africa may imperil millions
.
New York Times
. January 28,
2007
. Available at: http://www.nytimes.com/2007/01/28/world/africa/28tuberculosis.html?th&emc=th. (Accessed 2007 Jan 29)
2
World Health Organization
.
Global tuberculosis control: surveillance, planning, financing
. WHO Report 2006. Geneva,
World Health Organization
(WHO/HTM/TB/2006.362).
3
Trends in tuberculosis—United States, 2005
.
MMWR Morb Mortal Wkly Rep
  2006;
55
(
11
):
305
308
.
4
World Tourism Organization
.
“Another Record Year for Tourism.”
Press Release; January 29,
2007
. Available at: http://www.world-tourism.org/newsroom/Releases/2007/january/recordyear.htm. (Accessed 2007 Jan 30)
5
Cobelens
F
Van Deutekom
H
Draayer‐Jansen
I
, et al.
Risk of infection with Mycobacterium tuberculosis in travelers to areas of high tuberculosis endemicity
.
Lancet
 
2000
;
356
:
461
465
.
6
“Fast Facts.”
What is the Peace Corps?
Available at: http://www.peacecorps.gov/index.cfm?shell=learn.whatispc.fastfacts. (Accessed 2007 Jan 30)
7
Bernard
KW
Graitcer
PL
Van Der Vlugt
T
, et al.
Epidemiological surveillance in Peace Corps Volunteers: a model for monitoring health in temporary residents of developing countries
.
Int J Epidemiol
 
1989
;
18
:
220
226
.
8
American Thoracic Society
,
Centers for Disease Control and Prevention
.
Targeted tuberculin testing and treatment of latent tuberculosis infection
.
Am J Respir Crit Care Med
 
2000
;
161
(
Suppl
):
S221
S247
.
9
Global tuberculosis control—surveillance, planning, financing
.
WHO Report
.
2006
. Annex 1. Available at: http://www.who.int/entity/tb/publications/global_report/2004/annex1.pdf. (Accessed 2007 Jan 30)
10
Corbett
EL
Watt
CJ
Walker
N
, et al.
The growing burden of tuberculosis: global trends and interactions with the HIV epidemic
.
Arch Intern Med
 
2003
;
163
:
1009
1021
.
11
Freedman
DO
Weld
LH
Kozarsky
PE
, et al.
Spectrum of disease and relation to place of exposure among ill returned travelers
.
N Engl J Med
 
2006
;
354
:
119
130
.