Immigrants and the Spread of Tuberculosis in the United States: A Hidden Cost of Immigration by, Michael J. Greenwood and Watson R. Warriner.

Immigrants and the Spread of Tuberculosis in the United States:

A Hidden Cost of Immigration

by,Michael J. Greenwood

andWatson R. Warriner

Research Question and Motivation

Do immigrants from countries with high TB incidence affect Tuberculosis cases among the foreign-born

population, and in turn, is the native-born population in the United States infected?

• TB is the second largest killer from infectious diseases in the world• TB Prevalence is on the rise around the world• TB rates in the U.S. continue to decline, but by less each year• Does something have to give?• Is there transmission between cohorts?

Figure 1. TB Incidence Map (2006)

Figure 2. HIV Prevalence Map (2007)

Notes: Data obtained from the CDC Wonder OTIS Database and U.S. Census Bureau

Notes: Data obtained from World Health Organization Tuberculosis Programme

Notes: Data obtained from the CDC Wonder OTIS Database and U.S. Census Bureau

TB Background• Types– Latent or Active

• Treatments– Chemotherapy (four different drugs for 6 months)– BCG (Bacillus Calmette-Guerin) Vaccine – not

effective for active or re-activations• Immigration Laws– Persons with TB not allowed into the U.S.– Prior to 2007: chest x-ray (only detects active)– 2007 to Present: skin test for children under 15

(detects both active and latent forms)

Related Research• Little research regarding immigrant to native transmission

– Stagnation in TB elimination relatively recent– Immigration has not been a primary focus in TB elimination efforts

• Small-scale case studies vs. larger-scale epidemiological studies

• Conclusions– Positively correlated with TB:

• Number of minorities, population density, immigration, poverty, and HIV/AIDS

– Findings are inconsistent– No research on transmission to native-born populations

Theoretical Background

• Top 50 Metropolitan Statistical Areas (MSAs) by total TB cases (1993-2007)– Limitation due to suppression of TB statistics– Account for 69.5% of total TB cases in the U.S. (1993-2007)

• Observation = an MSA in a given year– 750 total (15 years x 50 MSAs)

Theoretical Background

• Recursive Model (A -> B, B -> C)– A: High-Incidence Immigration– B: Foreign-Born TB– C: Native-Born TB

1. FBTBit = f (HMIGit , LMIGit

, DEMit , SOCECONit)

2. NBTBit = g (FBTBit , DEMit , SOCECONit)

Data

1. Tuberculosis Statistics1. Constant geographies: 2007 MSA definitions

2. Demographic and socio-economic data

3. Country-specific TB incidence data

4. MSA immigration statistics

5. HIV incidence data

Table 3. Descriptive Statistics, All Variables from Pooled DataVariable Obs. Mean Std. Dev. Min Max

Number of Native TB Cases (Flow) 750 120 218 5 3,164Number of Foreign-Born TB Cases (Flow) 750 126 239 1 1,673

Total Immigrants (Flow) 750 14,279 27,159 382 224,427

Immigrants from Top 50 High TB Countries (Flow) 750 2,604 4,874 14 41,403

Total Population 750 2,905,694 3,086,156 439,320 18,815,988Native Born Population 750 2,417,600 2,278,708 322,556 13,487,097

Foreign-Born Population 750 488,094 891,794 13,335 5,328,891Males* 750 1,422,801 1,497,485 212,243 9,103,790

Females* 750 1,482,894 1,589,332 227,077 9,712,198Youth (Under 22 Years Old)* 750 901,056 938,848 181,916 5,441,926

Middle Age (Between 21 and 60 Years Old)* 750 1,558,658 1,662,414 193,379 10,027,211Seniors (Above 59 Years Old)* 750 445,981 499,923 57,285 3,346,851

Whites 750 1,740,128 1,629,987 55,684 10,251,089Blacks 750 409,482 538,430 1,097 3,145,815Asians 750 169,176 299,398 1,544 1,755,257

American Indians 750 10,499 11,274 257 78,438Other Races 750 57,931 70,131 834 499,688

Hispanics 750 518,479 893,002 8,161 5,675,443

Population Density (people per square mile) 750 644 551 71 2,798

Families earning under $25,000 per year (2007 $) 750 103,040 106,687 14,603 670,217

HIV Incidence (per 100,000) for 2003-2007 250 15 9 2 51

* Not in Regressions

Econometric Approach

• Five Estimations per Regression– FOCUS: Temporal and Divisional (9 Census Divisions) Fixed Effects

• Base Year = 1993, Base Division = Pacific

• Immigration Variable is Summed, t and t-1

• HIV/AIDS Incidence Inclusion– 2006, 12% TB cases in U.S. were also co-infections with HIV– Data Limited to 2003 – 2007 (Panel Data with 250 Observations)

– Only an estimated effect

Econometric Approach

• Double-log regression– Results can be interpreted as elasticities• Or…the percentage change in the dependant variable

that results from a one-percent change in the independent variable

• FBTBit = α1 (HMIGit β1) (LMIGit

β2 ) (FBPopit β3) (NBPopit

β4) (PopDenit β5) (Povertyit

β6)( εit )

2. NBTBit = α2 (FBTBit ρ1) (NBPopit

ρ2) (FBPopit ρ3 ) (Whiteit

ρ4 ) (Blackit ρ5 ) (Asianit

ρ6 ) (AmerIndit ρ7 )

(OtherRaceit ρ8 ) (Hispanicit

ρ9 ) (PopDenit ρ10 ) (Povertyit

ρ11 ) ( εit )

Table 4. Number of TB Cases among the Foreign-Born Population in U.S. Metropolitan Areas, 1993-2007: Double Logarithmic Estimates (β) and t-Ratios (t)

  (1) (2) (3) (4) (5)

VARIABLES ln(FBTB) ln(FBTB) ln(FBTB) ln(FBTB) ln(FBTB)           ln(Immigrants from Top 50 Inc. Countries) β: 0.174*** 0.259*** 0.242*** 0.270*** 0.287*** t: (5.825) (7.798) (3.410) (7.893) (7.980)ln(Immigrants from All Other Countries) 0.136*** 0.177*** 0.0535 0.143*** 0.0314

(2.881) (3.328) (0.764) (2.595) (0.581)ln(Foreign-Born Population) 0.818*** 0.731*** 1.498*** 0.739*** 0.841***

(16.40) (12.63) (6.748) (12.33) (12.71)

ln(Native Population) -0.122* -0.268*** 3.378*** -0.323*** -0.234***(-1.892) (-3.809) (3.005) (-4.624) (-3.597)

ln(Population Density) 0.0404* 0.0282 -4.901*** 0.0293 0.0824***(1.757) (1.361) (-3.595) (1.188) (3.337)

ln(Families in Poverty) -0.229*** -0.116* 0.478 -0.0466 -0.140**(-3.698) (-1.744) (1.015) (-0.753) (-2.178)

 Temporal Fixed Effects N Y Y Y Y

 Cross-Sectional Fixed Effects N N Y N N

 Regional Fixed Effects N N N Y N

 Divisional Fixed Effects N N N N Y

 Observations 750 750 750 750 750R-squared 0.914 0.924 0.960 0.925 0.940Robust t-statistics in parentheses*** p<0.01, ** p<0.05, * p<0.1

Table 5. Number of TB Cases among the Native-Born Population in U.S. Metropolitan Areas, 1993-2007: Double Logarithmic Estimates (ρ) and t-Ratios (t)

  (1) (2) (3) (4) (5)VARIABLES ln(NBTB) ln(NBTB) ln(NBTB) ln(NBTB) ln(NBTB)           ln(Foreign-Born TB Cases) ρ: 0.279*** 0.136*** 0.198*** 0.129*** 0.111*** t: (5.086) (3.296) (5.599) (3.334) (2.685)ln(Native Population) 0.187 0.114 1.843 -0.301** -0.0418

(1.016) (0.819) (1.152) (-1.989) (-0.272)ln(Foreign-Born Population) -0.407*** -0.305*** 0.663** -0.349*** -0.241**

(-4.407) (-4.355) (2.205) (-4.800) (-2.575)ln(Non-Hispanic Whites) -0.263** -0.369*** 0.366 -0.0138 -0.100

(-2.409) (-4.730) (0.768) (-0.177) (-1.218)ln(Non-Hispanic Blacks) 0.369*** 0.416*** 0.548** 0.232*** 0.234***

(14.12) (20.28) (2.395) (9.321) (7.179)ln(Asians) 0.271*** 0.123*** -0.923*** 0.299*** 0.179***

(5.202) (3.035) (-4.195) (5.962) (3.037)ln(American Indians) 0.149*** -0.0342 0.0144 -0.154*** -0.0576*

(4.359) (-1.145) (0.122) (-5.287) (-1.782)ln(Other Races, Including Multi-Racial) -0.549*** -0.0834* 0.127 -0.0106 -0.00415

(-10.90) (-1.828) (0.904) (-0.245) (-0.0928)ln(Hispanics) 0.104** 0.182*** -0.497** 0.129*** 0.134***

(2.279) (5.142) (-2.375) (3.582) (3.411)ln(Population Density) 0.191*** 0.106*** -2.012 0.0540 0.0774**

(4.315) (2.969) (-1.284) (1.563) (2.096)ln(Families in Poverty) 0.674*** 0.690*** 0.759* 1.017*** 0.758***

(7.138) (8.513) (1.939) (11.03) (7.237) 

Temporal Fixed Effects N Y Y Y Y 

Cross-Sectional Fixed Effects N N Y N N 

Regional Fixed Effects N N N Y N 

Divisional Fixed Effects N N N N Y 

Observations 750 750 750 750 750R-squared 0.748 0.853 0.954 0.879 0.879Robust t-statistics in parentheses*** p<0.01, ** p<0.05, * p<0.1

Table 6. Number of TB Cases among the Foreign-Born Population in U.S. Metropolitan Areas (HIV Incidence

Included), 2003-2007: Double Logarithmic Estimates (β) and t-Ratios (t)

  (5) (6)

VARIABLES ln(FBTB) ln(FBTB)     

ln(Imms. Of Top-50 Inc. Countries) β: 0.297*** 0.309*** t: (4.977) (5.170)ln(Imms. Of All Other Countries) -0.0826 -0.0888

(-0.858) (-0.919)ln(Foreign-Born Population) 0.911*** 0.913***

(7.995) (7.944)

ln(Native Population) -0.238** -0.250**

(-1.972) (-2.106)ln(Population Density) 0.112*** 0.113***

(2.615) (2.611)ln(Families in Poverty) -0.115 -0.0902

(-1.018) (-0.803)

ln(HIV Incidence Rate)   -0.0695

  (-1.430)

   Temporal Fixed Effects Y Y

   Cross-Sectional Fixed Effects N N

   Regional Fixed Effects N N

   Divisional Fixed Effects Y Y

   Observations 250 250

R-squared 0.940 0.941Robust t-statistics in parentheses*** p<0.01, ** p<0.05, * p<0.1

Table 7. Number of TB Cases among the Native-Born Population in U.S. Metropolitan Areas (HIV Incidence Included), 1993-2007:

Double Logarithmic Estimates (ρ) and t-Ratios (t)   (5) (6)

VARIABLES ln(NBTB) ln(NBTB)     

ln(Foreign-Born TB Cases) ρ: 0.172*** 0.136**

t: (2.603) (2.102)ln(Native Population) 0.0682 0.214

(0.309) (1.010)ln(Foreign-Born Population) -0.366** -0.502***

(-2.326) (-3.550)ln(Non-Hispanic Whites) -0.143 -0.153

(-1.182) (-1.317)ln(Non-Hispanic Blacks) 0.240*** 0.0834

(4.312) (1.388)ln(Asians) 0.265** 0.368***

(2.570) (3.556)ln(American Indians) -0.0173 0.0455

(-0.318) (0.824)ln(Other Races, Incl. Multi-Racial) -0.0944 -0.143*

(-1.215) (-1.775)ln(Hispanics) 0.137* 0.170***

(1.945) (2.754)ln(Population Density) 0.140** 0.137**

(2.315) (2.346)ln(Families in Poverty) 0.651*** 0.660***

(4.147) (4.001)ln(HIV Incidence Rate)   0.325***

  (4.198)   

Temporal Fixed Effects Y Y   

Cross-Sectional Fixed Effects N N   

Regional Fixed Effects N N   

Divisional Fixed Effects Y Y   

Observations 250 250R-squared 0.871 0.883Robust t-statistics in parentheses*** p<0.01, ** p<0.05, * p<0.1

Empirical Results

• Positive and significant elasticities for key independent variables in both regressions

• Increased immigration from high-TB incidence countries -> increased number of TB cases among the foreign-born -> more native-born TB cases

• Transmission exists from the foreign to the native-born populations in the sample

Societal Cost of TB in U.S. for 2008• Societal Cost Makeup

• $1.47 billion - $2.63 billion (not including transmission)– 0.018% of total GDP ($14.61 trillion)

• TST for all Legal Permanent Resident Immigrants = $23.8 million– Between 0.90% and 1.62% of total TB cost

• Minor relative cost to eliminate incoming TB

Discussion

• Advantages• Broad sample and isolation of urban areas

• Limitations• Linear interpolation of demographic data• Demographic data only gathered for entire population• Immigration data only include Legal Permanent Residents

• Extensions• Two way transmission – two staged least squares• Obtain more years for HIV incidence data

Implications of Research

• Incoming latent TB among Immigrants infecting the natives through transmission via the foreign-born population

• TST for all immigrants highly recommended

• HIV Travel Ban Lifted in 2009– Major Implications to this study– 1/3 of those infected with HIV are TB co-infections