Infectious Diseases
Infectious diseases will always be with us. But in previous centuries, they were the major causes of death, both during wars, and during peace. It was not until the late 19th century that the germ theory of disease became firmly established. Virus disease was not recognized until into the 20th century. With recognition of micro-organisms came great advances in public health to control the spread of diseases. Early attempts at immunization against common diseases, particularly smallpox, were successful even without knowing the bacterial or viral basis for diseases. The late 19th century saw the development of more and better vaccines, notably against typhoid fever and tetanus. Other diseases such as malaria and yellow fever, could be controlled by identifying the insect vectors and either eliminating or controlling them. Prophylaxis against malaria was available, and routinely used. In many ways, the years before World War 1 marked the beginning of the conquest of infectious diseases. But only the beginning. In 1917, antibiotics were still 20 years in the future. Most of today’s vaccines had not yet been developed. Many among the general public knew nothing of prevention. Death from such diseases as tuberculosis and bacterial pneumonia were common by today’s standards. Overall, disease caused more deaths in the American Army than did enemy action.
As in previous wars, the training camps in the United States were breeding grounds for disease. The major childhood diseases, measles, mumps, and chicken pox, could sweep through a camp. More serious diseases such as meningitis and pneumonia were a constant threat. 
Camp Merritt, NY
Recruits were screened for infectious diseases at entry, which helped somewhat. Colds, “flu”, and influenza were a constant problem, with secondary pneumonia carrying a real risk of death. Bacterial pneumonia, at this time, carried a 40-50% mortality. Without antibiotics, all that could be done was general supportive care. Until the advent of the H1N1 influenza epidemic of “Spanish flu,” simple seasonal influenza was rarely fatal. But the new influenza, appearing in 1918, proved to have a mortality rate in the 2-3% range. If 1000 soldiers contracted it, 50 to 100 would go on to “pneumonia”, and 25 to 50 would die. (See below)
This discussion of infectious diseases is focused on the American Expeditionary Force (AEF), that is, the troops in Europe. Many of these soldiers arrived in Europe already ill. Troop ships crossing the Atlantic in 7 to 15 days were packed full of troops in close quarters. Especially when the influenza epidemic began, it would prove nearly impossible to control disease outbreaks on ships. Once ashore, conditions were not greatly improved. Units were taken to makeshift training camps scattered throughout southern and central France, and lived under conditions which were not much less crowded than the troopships.
Crowded Troopship, Newport News, VA
The impact of the childhood diseases should not be overlooked. Many soldiers came from remote areas and farms in the U.S. They may have been particularly vulnerable to such illnesses. Vaccinations to these diseases did not exist. Even after reaching Europe, soldiers continued to fall ill to the diseases of children. In terms of days lost, the most important disease was mumps. There were 82,000 cases recorded in the AEF, with only 43 deaths, but with 1 million days lost to illness. There were 8200 cases of measles, with 86 deaths. Diphtheria struck 4700 soldiers, with 62 deaths.
Meningococcal meningitis is particularly deadly. The disease can spread in populations of young people living in crowded conditions. The AEF recorded 1965 cases, with 911 deaths.
Other communicable diseases were present in the AEF. Typhoid fever claimed 1200 cases, with 155 deaths. Yet this was a major advance over previous wars. The infection rate in the Spanish-American war was 142/1000 soldiers, but less than 1 per 1000 in the AEF. Typhoid vaccine was available, and shots were mandatory for soldiers going overseas. 
Typhoid Inoculation was Routine for All Soldiers
Smallpox, despite near-universal vaccination, still counted for 30 cases, with 5 deaths. Malaria, while not often fatal, was seen in 850 cases, with 4 deaths. Dysentery, the scourge of armies in past centuries, was still present, but kept largely in check by sanitary measures. There were 6200 cases, and 31 deaths.
Tuberculosis, still a major disease at this time, was partly eliminated by screening. The Army wouldn’t accept any recruit with TB, and would discharge any soldier who developed it. Overall, it was estimated that 10,000 soldiers served with TB. Screening was done by physical examination, and was much less effective than the mass use of chest x-rays. The disease was endemic in the civilian populations of the day. Death from TB had been declining during the entire 19th century, but there was an increase during the war among civilian populations. Figures from the Army medical department showed that 4200 cases were recorded in the AEF, with 433 deaths.
Trench conditions were awful. Poorly nourished, living in trench conditions, soldiers of all armies were susceptible to all of the epidemic diseases, and others besides. Most American troops spent relatively little time in the trenches, and were spared the worst of trench diseases. (see below)
Venereal diseases, primarily syphilis and gonorrhea, were a chronic problem for all armies, and the AEF was no exception. Control of venereal diseases was primarily prevention. There were treatments for syphilis, but these involved mercury compounds, toxic in themselves. Gonorrhea could be treated, somewhat ineffectively, with local antiseptics, a process best left undescribed. The antibiotic treatments which have relegated these scourges to mere annoyances didn’t exist, and treatment was primarily a matter of waiting for them to heal. Venereal disease was a serious discipline problem, which meant that the medical system became involved with the Army judicial system. Neither the doctors nor the lawyers were happy with this involvement.
Savenay Hospital Center, France
Death from any of these infectious diseases is a relatively rare event today. Or at least, in America, and in most Western countries. A century ago, it was not so. Tuberculosis, while declining, was still known as the “captain of all these men of death”. Pneumonia was a common cause of death. For example, John McCrae, the Canadian surgeon-soldier who wrote “In Flanders Fields”, died of pneumonia in January, 1918. Small children regularly died of infections. While all of these were beginning to come under control by the early 20th century, people still lived with infectious death as a regular occurrence. So, while many soldiers died of diseases, this was not viewed at the time as a failure of the medical system. Instead, the rate of disease deaths was seen as low relative to the previous century. The medical system, and particularly the preventive measures taken by the American army, we considered to have done an acceptable, even admirable, job in controlling infectious disease.
Then, there was trench foot. This was a condition brought about by constant immersion in cold water, without chances to dry off. Technically, this was a cold injury rather than an infection, but secondary infection usually appeared if the injury was not treated. Trench foot was a constant source of troops having to be evacuated, and affected all armies more or less equally. The American army recorded 1800 cases during 1917-18, although only 5 deaths.
against it, and all of the other strains of influenza. We can give antibiotics for the secondary pneumonia. And we can support patients with ventilators if their lungs fail. But in 1918, all physicians could do was to support the patient, quarantine as best they could, and ride out the epidemic. 
