Tuberculosis Risk in US Peace Corps Volunteers, 1996 to 2005

Paul Jung MD, MPH, Richard H Banks MA
DOI: http://dx.doi.org/10.1111/j.1708-8305.2008.00184.x 87-94 First published online: 1 March 2008

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.

View this table:
Table 1

Peace Corps countries—Europe and Central Asia

Peace Corps countryYears as Peace Corps countryMonths with Volunteers, 1996–2005Total Volunteer‐yearsTotal PPD conversionsPPD conversion rate per 1,000 Volunteer‐monthsTotal active TB casesActive TB rate per 1,000 Volunteer‐months
Albania1996–200542208.42472.79900.000
Armenia1996–2005117674.626192.34700.000
Azerbaijan2003–200527113.10310.73700.000
Bulgaria1996–20051191,212.449231.58100.000
Czech Republic1996–19971772.73100.00000.000
Estonia1996–200275230.53031.08400.000
Georgia2001–200556208.32910.40000.000
Hungary1996–1997990.68065.51400.000
Jordan1997–200590393.35030.63600.000
Kazakhstan1996–20051201,133.749332.42620.147
Kyrgyzstan1996–2005115746.023151.67610.112
Latvia1996–200278264.02530.94700.000
Lithuania1996–200279292.75651.42300.000
Macedonia1998–200570257.82341.29300.000
Moldova1996–2005120943.721171.50100.000
Mongolia1996–2005119738.650101.12800.000
Poland1996–200166742.25650.56110.112
Romania1996–20051191,337.673100.62300.000
Russia Western1996–200385538.321172.63200.000
Slovakia1996–200279512.23571.13900.000
Turkmenistan1996–2005114619.556182.42110.135
Ukraine1996–20051202,057.117281.13400.000
Uzbekistan1996–2005106882.207121.13410.094
Total14,270.3342471.44260.035
  • PPD = purified protein derivative; TB = tuberculosis.

View this table:
Table 2

Peace Corps countries—East Asia and South Asia

Peace Corps countryYears as Peace Corps countryMonths with Volunteers, 1996–2005Total Volunteer‐yearsTotal PPD conversionsPPD conversion rate per 1,000 Volunteer‐monthsTotal active TB casesActive TB rate per 1,000 Volunteer‐months
Bangladesh1998–200577323.43930.77300.000
China1996–2005106478.283162.78810.174
East Timor2002–20054392.92310.89700.000
Nepal1996–20041041,091.636241.83200.000
Philippines1996–20051201,216.55960.41100.000
Russia Far East1996–200384388.56971.50100.000
Sri Lanka1996–1998, 20053472.62100.00000.000
Thailand1996–2005120733.574151.70400.000
Total4,397.604721.36410.019
  • PPD = purified protein derivative; TB = tuberculosis.

View this table:
Table 3

Peace Corps countries—Africa

Peace Corps countryYears as Peace Corps countryMonths with Volunteers, 1996–2005Total Volunteer‐yearsTotal PPD conversionsPPD conversion rate per 1,000 Volunteer‐monthsTotal active TB casesActive TB rate per 1,000 Volunteer‐months
Benin1996–20051191,018.82880.65400.000
Botswana1996–200558228.65731.09310.364
Burkina Faso1996–2005120808.225151.54700.000
Cameroon1996–20051191,315.513493.10460.380
Cape Verde1996–2005120449.84040.74100.000
Central African Republic1996539.19012.12612.126
Chad1996–1998, 2003–200555140.56121.18610.593
Congo1996–19971364.25511.29700.000
Cote d’Ivoire1996–200281764.635293.16110.109
Eritrea1996–199829103.75621.60600.000
Ethiopia1996–199936123.14353.38410.677
Gabon1996–2005114674.95100.00000.000
Gambia1996–2005119825.97160.60500.000
Ghana1996–20051201,478.360120.67620.113
Guinea1996–2005120988.260131.09600.000
Guinea‐Bissau1996–19982894.18865.30910.885
Kenya1996–20051201,340.830402.48620.124
Lesotho1996–2005119863.461212.02730.290
Madagascar1996–2005114811.025161.64410.103
Malawi1996–20051201,094.935231.75020.152
Mali1996–20051191,580.000593.11210.053
Mauritania1996–2005120647.83370.90000.000
Morocco1996–20051151,282.116181.17010.065
Mozambique1998–200587380.62440.87600.000
Namibia1996–20051191,022.160141.14110.082
Niger1996–20051201,109.848211.57700.000
Sao Tome199679.81000.00000.000
Senegal1996–20051201,325.692110.69100.000
South Africa1997–2005107763.77060.65500.000
Swaziland1996, 2003–200539132.41121.25900.000
Tanzania1996–20051201,100.860110.83310.076
Togo1996–2005120898.913111.02000.000
Tunisia (Malta)1996621.67600.00000.000
Uganda1996–1999, 2001–200598384.62771.51700.000
Zambia1996–20051201,129.342120.88510.074
Zimbabwe1996–200171371.65271.57000.000
Total25,389.9184461.464270.089
  • PPD = purified protein derivative; TB = tuberculosis.

View this table:
Table 4

Peace Corps countries—Central America

Peace Corps countryYears as Peace Corps countryMonths with Volunteers, 1996–2005Total Volunteer‐yearsTotal PPD conversionsPPD conversion rate per 1,000 Volunteer‐monthsTotal active TB casesActive TB rate per 1,000 Volunteer‐months
Belize1996–2005120576.35920.28900.000
Costa Rica1996–2005120489.24620.34100.000
El Salvador1996–20051201,078.850141.08110.077
Guatemala1996–20051201,997.848361.50220.083
Honduras1996–20051202,205.426321.20910.038
Mexico2004–20051517.50900.00000.000
Nicaragua1996–20051191,486.968432.41020.112
Panama1996–20051201,059.65270.55010.079
Total8,911.8581361.27270.065
  • PPD = purified protein derivative; TB = tuberculosis.

View this table:
Table 5

Peace Corps countries—Caribbean

Peace Corps countryYears as Peace Corps countryMonths with Volunteers, 1996–2005Total Volunteer‐yearsTotal PPD conversionsPPD conversion rate per 1,000 Volunteer‐monthsTotal active TB casesActive TB rate per 1,000 Volunteer‐months
Dominican Republic1996–20051201,560.879281.49500.000
Eastern Caribbean1998–2005961,043.81110.08000.000
Haiti1996–2005103395.89351.05200.000
Jamaica1996–20051201,024.572141.13910.081
Total4,025.155480.99410.021
  • PPD = purified protein derivative; TB = tuberculosis.

View this table:
Table 6

Peace Corps countries—South America

Peace Corps countryYears as Peace Corps countryMonths with Volunteers, 1996–2005Total Volunteer‐yearsTotal PPD conversionsPPD conversion rate per 1,000 Volunteer‐monthsTotal active TB casesActive TB rate per 1,000 Volunteer‐months
Bolivia1996–20051201,554.401170.91100.000
Chile1996–199831111.45821.49500.000
Ecuador1996–20051201,619.600211.08110.051
Guyana1996–2005119414.842132.61100.000
Paraguay1996–20051201,957.38520.08500.000
Peru2002–200541225.54100.00000.000
Suriname1996–2005120365.17510.22800.000
Uruguay1996–19971169.06800.00000.000
Total6,317.470560.73910.013
  • PPD = purified protein derivative; TB = tuberculosis.

View this table:
Table 7

Pacific Island Peace Corps countries

Peace Corps countryYears as Peace Corps countryMonths with Volunteers, 1996–2005Total Volunteer‐yearsTotal PPD conversionsPPD conversion rate per 1,000 Volunteer‐monthsTotal active TB casesActive TB rate per 1,000 Volunteer‐months
Fiji (Tuvalu)1996–1997, 2003–200550202.77352.05500.000
Kiribati1996–2005118438.90520.38010.190
Marshall Island199653.08800.00000.000
Micronesia1996–2005119567.00310.14700.000
Papua New Guinea1996–200166388.24910.21500.000
Samoa (Niue)1996–2005114555.18160.90110.150
Solomon Island1996–200054289.56910.28800.000
Tonga1996–2005120567.00650.73510.147
Vanuatu1996–2005120490.93220.33900.000
Total3,502.706230.54730.071
  • 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.

View this table:
Table 8

Peace Corps Volunteers in high‐incidence countries

Peace Corps countryYears as Peace Corps countryMonths with Volunteers, 1996–2005Total Volunteer‐yearsTotal PPD conversionsPPD conversion rate per 1,000 Volunteer‐monthsTotal active TB casesActive TB rate per 1,000 Volunteer‐months
Bangladesh1998–200577323.43930.77300.000
Botswana1996–200558228.65731.09310.364
China1996–2005106478.283162.78810.174
Congo1996–19971364.25511.29700.000
Ethiopia1996–199936123.14353.38410.677
Haiti1996–2005103395.89351.05200.000
Kenya1996–20051201,340.830402.48620.124
Lesotho1996–2005119863.461212.02730.290
Malawi1996–20051201,094.935231.75020.152
Mozambique1998–200587380.62440.87600.000
Namibia1996–20051191,022.160141.14110.082
Philippines1996–20051201,216.55960.41100.000
Russia Far East1996–200384388.56971.50100.000
Russia Western1996–200385538.321172.63200.000
South Africa1997–2005107763.77060.65500.000
Tanzania1996–20051201,100.860110.83310.076
Thailand1996–2005120733.574151.70400.000
Uganda1996–1999, 2001–200598384.62771.51700.000
Zambia1996–20051201,129.342120.88510.074
Zimbabwe1996–200171371.65271.57000.000
Total12,942.9542231.436130.084
  • 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.

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

View Abstract