Why Did Black Soldiers Historically Have More Pneumonia Than White Soldiers in the U.S. Army?

ABSTRACT.

Black U.S. Army soldiers had four times as much bacterial pneumonia as White U.S. Army soldiers during both the U.S. Civil War and World War I (WWI). Pneumonia case fatality rates were a third greater in Black soldiers during the U.S. Civil War, but were the same between the racial groups by WWI. During WWII, the use of antibiotics decreased bacterial pneumonia mortality rates 100-fold and apparently erased racial differences. Similar differences in bacterial pneumonia rates by racial group were observed in African colonial soldiers of the French and British Armies during WWI. Pneumonia rates in Indian, Filipino, and Puerto Rican soldiers suggested that genetic polymorphisms were not a decisive factor determining Black pneumonia mortality. Postmeasles pneumonias did not suggest an immune deficit in Black soldiers. Geographic focus of pneumonia in Black soldiers from the southern U.S. states and other tropical regions raises the possibility that increased bacterial pneumonia rates were related indirectly to malaria infections. Malaria remains a difficult-to-measure but potentially important mortality risk factor in pneumonia.

A striking instance of the greater prevalence of pneumonia among negroes, especially those from southern rural districts as compared with white men, is shown by certain figures obtained from Camp Funston.¹

Unexplained historical observations may provide important insights into pathological processes that are no longer investigated easily. Four times the number of Black soldiers developed bacterial pneumonia in the U.S. Army during both the U.S. Civil War (1861–1865) and World War I (WWI) (1917–1918) than their White soldier comrades despite receiving the same medical care, housing, and rations.^2,3 There was a distinct southern geographic focus to this apparent racial vulnerability, and rural isolation may have played some role as denoted by a high measles incidence. Comparison to other soldiers of the same era either in the U.S. Army (Filipino, Puerto Rican) or colonial soldiers of the French or British/Indian armies does not indicate that race per se was a decisive factor in pneumonia rates. When antibiotics became widely available during WWII (1941–1945) racial differences in pneumonia rates largely disappeared, making embedded social prejudices a very unlikely explanation of the previously observed mortality differences.⁴ Although race is now seen as a social construct and not a genetic entity, its historical importance in military groups allows one to investigate what might have explained the striking differences between Black and White soldiers’ pneumonia rates. This divergence was appreciated at the time, as noted in the quote at the beginning of this article. Emphasizing the distinct geographic, rather than racial, focus of the increased pneumonia risk suggests that other infectious diseases such as malaria may have been involved indirectly.

During the U.S. Civil War, Black soldiers had at least four times the rate of pneumonia and much greater mortality rates than White soldiers of the same Union Army² (Table 1^5–9). Black soldiers were referred to as United States Colored Troops (USCTs), of whom more than 180,000 enlisted and 36,000 died of all causes during the war; more than 85% deaths were the result of disease.^2,10 Although USCTs were not regarded as socially or militarily equal during the Civil War, and often were assigned less desirable duty stations, they did receive the same medical care, housing, and rations as White soldiers by military regulation.¹¹ After the Civil War, the U.S. Army reverted to its much-reduced frontier/colonial organization, and pneumonia was then a much smaller problem in seasoned soldiers. Black soldiers still experienced greater rates (up to 2-fold) of pneumonia than White or Filipino soldiers in the decade prior to WWI⁵ (Supplemental Figure 1¹²).

Table 1.

Pneumonia morbidity and mortality in U.S. Army and other military groups for which simultaneous measurements were available from different racial groups

Conflict, year	Black soldiers	White soldiers	Ratio	Reference
U.S. Civil War, 1862–1866	27.3/1,000 mortality; CFR, 32%	6.2/1,000 mortality; CFR, 24%	4.4	Woodward et al.2
U.S. Army, World War I, 1917–1919	11.6/1,000 mortality; CFR, 21%	3.0/1,000 mortality; CFR, 23%	3.9	Ireland3
U.S. Army, World War I, 1917–1919	56.1/1,000 morbidity	12.7/1,000 morbidity	4.4	Ireland,3 Ireland5
Indian Army, India, 1917	21.8/1,000 morbidity; CFR, 22.9% (Indians)	2.8/1,000 morbidity; CFR, 12.9% (Indians)	7.8	Mitchell and Smith6
French Army, Europe, 1917–1918	50–60/1,000 morbidity; CFR, 50%	–	10	Government of India7
French Army, West Africa, 1929–1936	12.8/1,000 morbidity; CFR, 16%	1.3/1,000 morbidity	10	Borrel8
British Army, West Africa, 1944	21.4/1,000 morbidity	1.9/1,000 morbidity	11	Eyre and Lowe9

CFR = case fatality rate. During World War I, the more specific lobar pneumonia diagnosis was used by the U.S. Army. As a result of differing diagnostic criteria, one can only compare groups approximately across different armies, but comparison within the same military group is reliable because the same medical officers were collecting consistent data from all racial groups.

World War I saw a massive expansion of the U.S. Army to more than 2 million soldiers, of which ∼13% were Black.³ During WWI, the 4-fold racial difference in lobar pneumonia rates first noted during the Civil War resumed, but the case fatality rates equalized (Table 1). U.S. Army officers recruited from the U.S. Census Bureau took great care collecting demographic and disease data using an early punch card system that predated any electronic data storage, which are the basis of all U.S. Army Surgeon General Reports used here.^3,5 State of birth was of great interest to the U.S. Census and thus got included in U.S. Army demographic data, such that one can calculate separate lobar pneumonia rates for both Black and White soldiers for each U.S. state (Figure 1A^13,14). Black and White pneumonia rates by state correlate, noting that pneumonia was particularly a problem of the soldiers born in U.S. states on the Gulf Coast, along with Arkansas.⁵ Vaughn et al.¹ noted that Black soldiers from Mississippi had four times the pneumonia incidence of Blacks from Missouri in the same recruit camp in Kansas, emphasizing the geographic nature of the increased pneumonia risk.

Figure 1.

(A) Lobar pneumonia (cases per 1,000 men) in both Black and White soldiers in the U.S. Army from 1917 to 1919 were divided by U.S. state of nativity, with the resulting correlation curve. Red dots mark the greater incidence in Gulf Coast (plus Arkansas) U.S. states.³ (B) Measles and lobar pneumonia (cases per 1,000 men) in the U.S. Army from 1917 to 1919 were divided by U.S. state of nativity, with the resulting correlation curve. Red dots mark the greater incidence Gulf Coast (plus Arkansas) U.S. states.^3,5 (C) Pneumonia morbidity (cases/1,000 persons) reported in civilians to U.S. public health authorities in 1931, divided by Black and White racial groups. Red dots mark Gulf Coast states similar to (A) and (B), without the same number of U.S. states having extant civilian data.^1,13 (D) Relative disease incidence in the British Army in Southeast Asia during 1945, where rates of pneumonia, tuberculosis, and malaria in British soldiers are considered as baseline compared with similarly collected morbidity information from soldiers in collocated Indian, East African (Kenya and Tanganyika) and West African (Nigeria, Gold Coast) military units.¹⁴

Two other respiratory infections complicate any interpretation of bacterial pneumonia rates in soldiers during WWI: measles and influenza. Measles was a major military medical problem during WWI and a good indicator of previous epidemiological isolation.¹⁵ Interestingly, Black and White U.S. Army soldiers had equal measles rates (19.58/1,000 versus 19.04/1,000), but the progression after measles infection to both lobar (0.44/1,000 versus 0.23/1,000) and bronchopneumonia (1.08/1,000 versus 0.72/1,000) was greater in Black soldiers than in Whites.^3,5 There is a good correlation between measles infection and lobar pneumonia when calculated by U.S. state of birth (Figure 1B). This is partially a reflection of rural southern states being more isolated socially during the early 20th century than other more urban regions, where soldiers were infected with measles at an earlier age. Many pneumonia cases followed an earlier influenza infection, with the 1918 influenza pandemic overlapping the end of WWI.¹⁶ Influenza infections during 1918 were equally common in Black and White U.S. Army soldiers (359/1,000 versus 361/1,000).³ The data from the 1918 influenza pandemic are complex; but, if anything, White soldiers suffered more from influenza toward the later part of 1918 than Black soldiers.¹⁷ Therefore, increased bacterial pneumonia rates in Black soldiers cannot be explained by measles or influenza infections because the two viral infections were distributed equally by racial group.

Further information was sought to compare the U.S. Army pneumonia rates during WWI to contemporary civilian records. Figure 1C¹³ shows data from fewer U.S. states that had pneumonia morbidity information by racial group from 1931. Note that the civilian data would not be restricted to the military cohort (∼20- to 40-year-old men), diagnostic criteria likely differed among states, and there was no notable geographic increase in pneumonia in southern states. Vaughn et al.¹ reproduced Metropolitan Life Insurance data (an admittedly economically biased information source) for 1911 to 1916, showing that racial differences between Black and White civilians had a ratio of about 2:1 in young adults, whose pneumonia rates were less than 1/1,000. So the military and civilian records did show consistently greater pneumonia rates in Blacks than Whites in the early 20th century, but the soldiers had much greater rates and ratios overall.

The U.S. Army of the early 20th century (<200,000 soldiers) was still a frontier/colonial-era military, with distinct racially defined regiments of Black, Filipino, Puerto Rican, and Hawaiian soldiers. During WWI, Filipino U.S. Army soldiers’ pneumonia rate was 10.2/1,000 compared with 1.4/1,000 (ratio, 7.3) in collocated White soldiers. Pneumonia rates are not available separately for Puerto Rican and Hawaiian soldiers, but total disease mortality (of which pneumonia would have been a major component) rates were calculated. While guarding the Panama Canal during WWI, Puerto Rican soldiers’ disease mortality was 13.7/1,000 compared with 3.0/1,000 (ratio, 4.5) in collocated White soldiers. Hawaiian soldiers’ disease mortality rate in Hawaii during WWI was 4.6/1,000 compared with 1.2/1,000 (ratio, 3.8) in collocated White soldiers. Therefore, pneumonia rate differences were seen in other racial groups within the U.S. Army in addition to the more numerous Black soldiers.

The French and British Imperial armies also had colonial era regiments that were defined racially and consisted of African or Indian soldiers (Table 1). Unlike the U.S. Army, which calculated pneumonia rates based on individual reports of sick soldiers, French and British military disease reports are based on entire units. Other issues making direct comparison with U.S. Army data difficult are differing clinical definitions of pneumonia, language translation, and reporting formats. However, some WWI colonial regiments had very serious pneumonia disease rates that limited the use of African and Indian units on the European battlefields. Pneumonia rates in African soldiers of the British Army in East Africa during WWI (30–50/1,000; case fatality rate, ∼25%) were 10 times those of units in Europe and were thought to be possibly associated with high malaria rates.⁶ Indian Army units in India during WWI had more than seven times the pneumonia rates and greater case fatality rates of collocated British battalions⁷ (Table 1). The French Army conscripted large numbers of African soldiers during WWI and was very concerned about the high pneumonia morbidity and mortality rates that continued into the postwar period and limited the use of Black soldiers in France.^8,18 Increased pneumonia rates were not only a concern for African and Indian soldiers; British medical officers were forced to make separate quarantine camps in England for New Zealand Army battalions because of their recognized susceptibility to respiratory infections as a result of their previous epidemiological isolation.⁹ Some of the racial differentials seen in British Army units during WWI continued 20 years later, even after the introduction of antibiotics. In West Africa (Nigeria, Gold Coast) in 1944, African soldiers had pneumonia rates of 21.4/1,000 compared with collocated British soldiers with pneumonia rates of 1.9/1,000 (ratio, 11).¹⁴ Figure 1D shows that pneumonia rates in Indian, East African, and West African soldiers during the Burma Campaign of 1945 were considerably greater than collocated British units. Racial differentials with pneumonia were distinctly different from similarly calculated rates of tuberculosis and malaria.¹⁴

Given these data, how does one then explain the decades of increased pneumonia rates in Black soldiers of the U.S. Army, which is now only of historical interest? Although race was understood to be the obvious answer in the early 20th century, this is not a currently viable hypothesis given the similar pneumonia rates in other colonial-era armies of different racial composition. Previous epidemiological isolation does explain some susceptibility to respiratory infections, particularly in military recruit camps, but it cannot be a large component in the U.S. Army because there were no racial differentials in measles and influenza rates. Social determinants such as access to medical care, quality of housing, and nutrition do play an important role in respiratory infections. In the military situation, however, mandated equal access to medical care, barracks, and rations largely controlled such variables. Genetic polymorphisms causing susceptibility to Pneumococcus seem a very unlikely explanation because of the large mortality ratios involved and the rapid disappearance of racial differences in pneumonia mortality in the antibiotic era.

Could coinfections with other infectious diseases have altered Black U.S. Army soldiers’ resistance to pneumonia? British medical officers certainly thought that extreme pneumonia mortality rates, particularly in the civilian carrier corps of East Africa during WWI, might have been a result of concomitant malaria.⁶ South African miners in their military-style barracks also had extremely high pneumococcal pneumonia rates, but Black miners recruited from the “tropics” (Malawi, Zambia) had much greater pneumonia mortality rates (26.3/1,000 versus 8/1,000; ratio, 3.3) than genetically similar Black South Africans recruited from areas of very low malaria endemicity.¹⁹ Only recently has it been appreciated that plasmodia may be long-term infectors of the reticuloendothelial system even without detectable parasitemia.²⁰ Dysfunction of the spleen certainly enhances pneumococcal mortality, but is there any evidence that malaria coinfections enhanced mortality as a result of pneumonia or other common infectious diseases? Decades of consistently collected epidemiological information in the Andaman Islands prison camps showed that malaria probably caused many more indirect deaths in Indian prisoners than those attributed acutely to malaria.²¹ When Christophers²² compared spleen weight (all prisoner deaths required postmortem examinations) in those dying of pneumonia in the Andaman Islands, his conclusion was that malaria played a large role in pneumonia mortality. This is a testable hypothesis. Archived pathology specimens (including spleens) exist from many U.S. soldiers who died of pneumonia during WWI and have been essential in reconstructing the genome of the 1918 influenza virus.¹⁶ Advances in genomic technology would allow modern researchers to look for evidence of otherwise undocumented malaria infections that might explain the remarkable southern geographic focus of lobar pneumonia in Black U.S. soldiers during WWI. Positive findings of plasmodial genomic material from Black U.S. soldier autopsies would have important implications for current infectious disease mortality studies in Africa and could further justify the elimination of all plasmodia infections, especially those that relapse through latent tissue parasites.

Note: A supplemental figure appears at www.ajtmh.org.