Primary Pneumonic Plague Transmission in the USA, 1900-2009

Pneumonic plague is a difficult phenomenon to model. We really don’t have much data from the modern medical era. Hinckley et al. (2012) argue that most of the data studied to date has been biased by taking it from well-established epidemics. To better study all transmission conditions, they gathered all of the cases of primary pneumonic plague in the United States between 1900 and 2009. Their data set, divided into pre- and post-antibiotic era, is really what interests me the most.

The demographics of the two eras tell very different stories. There were 60 cases before 1943, 92% of which occurred in California, 86% in three epidemics (San Francisco 1904, Oakland 1919, and Los Angles 1924). A full 83% of these cases came from documented human contact. After 1943, there have only been 14 cases from south-western states. Of these, 64% came from animal contact and another 21% from laboratory exposure. None of the post-1943 set obtained the infection from human contact. Obviously, the use of antibiotics is not the only difference between these two sets. Sheer number of cases and source of infection are very different.

In both data sets, the overwhelming number of cases failed to transmit the infection. In the antibiotic era, there have been no documented cases of human-to-human transmission of pneumonic plague in the US. On the other hand, in the pre-antibiotic era, where most cases come from epidemics, 8% of the cases transmitted to two or more people.

When it comes to pneumonic plague, antibiotics are not the panacea that is usually implied. In the antibiotic era, the mortality rate was “only 36%”, down from 92% in the pre-antibiotic era. So in other words, pneumonic plague today has approximately the same mortality rate as smallpox. Comforting.

Their models suggest that in the vast majority of instances pneumonic plague quickly reaches extinction due to poor transmission with traditional control measures. The important caveat is that super spreading events early in the outbreak can lead to an explosive increase in case numbers. In one case from 1924 Los Angles, one man transmitted pneumonic plague to 26 others. With the primary concern in the United States being bioterrorism,  response planning for a large plague outbreak will continue with the goal of identifying and containing super spreaders as soon as possible, while knowing that most cases will fail to transmit to anyone.

Reference:

 Hinckley AF, Biggerstaff BJ, Griffith KS, & Mead PS (2012). Transmission dynamics of primary pneumonic plague in the USA. Epidemiology and infection, 140 (3), 554-60 PMID: 21733272

Historic Meanings of “Cholera”

Today the term cholera is restricted to suspected infections caused by Vibrio cholerae, sometimes called Asiatic cholera. Vibrio cholerae produces a very characteristic watery diarrhea sometimes described as ‘rice water’. This narrow definition wasn’t always so.

Since antiquity, cholera could refer to any diarrhea or dysentery. The term cholera comes from the Greek word cholē meaning bile. Cholera then was a flushing of bile from the body in an attempt to rebalance Galen’s four humors of the body (blood, bile, black bile, and phlegm) [1].

In 19th century American medical records,  it is common to see three types of cholera reported: cholera morbus, cholera infantum, and Asiatic cholera. Cholera morbus and cholera infantum were both terms for non-specific diarrhea and/or dysentery in adults and children under age five respectively.  Cholera morbus was sometimes called the summer complaint and was usually found in older children and adults from July to September [2]. It was caused by a variety of gastrointestinal pathogens with a significant contribution from contaminated food. Cholera infantum was given as the primary cause of death in children under age five in 19th century Illinois [2]. Physicians specifically associated it with the ages of teething and finger foods. Even given its non-specific definition, it was still probably over diagnosed due to paradigms of childhood illness. For example, early Illinois physicians  did not believe that children could contract malaria, then endemic in Illinois. Asiatic cholera is caused by Vibrio cholerae, epidemic in Illinois in 1832-1834, 1838, 1849-1852, 1866-1867, and 1892 [2]. Apart from discrete epidemic waves, Asiatic cholera was uncommon in America.

References:

[1] Männikkö, N. (Ed) (2011). Etymologia: Cholera. Emerging Infectious Disease, 17 (11) http://dx.doi.org/10.3201/eid1711.ET1711

[2]  Rawlings, Issac D. et al. (1927).The Rise and Fall of Disease in Illinois. State Department of Health.

Cholera in Illinois’ American Bottoms Region, 1849

This year is turning out to be a bad year for cholera. Major cholera outbreaks have erupted in Haiti, Pakistan, and in several African countries. Reports of all these outbreaks remind me of cholera epidemics in American history. In the 19th century cholera wasn’t as closely linked with disasters as it is today. Back then cholera was transmitted best by urban water systems, although it still swept through rural areas as well.

The 1850  federal mortality census  gives us a glimpse at the cholera epidemic that struck Illinois  during the summer of 1849. The American Bottoms region is the four counties in the St. Louis Metro East: Madison Co., St Clair Co, Monroe Co, and Randolph Co. It runs along the eastern shore of the Mississippi River from Alton to Kaskaskia. In 1849 the American Bottoms was mostly rural with a few good size towns (Alton, East St. Louis, Belleville, Cahokia). It is not hard to see the epidemic in a graph of deaths vs. months of 1849-1850.

From a slide presentation I did a few years ago. The American Bottoms region is the four counties now referred to as the St Louis Metro East.

In the mid-19th century summer was always the most deadly time of year in Illinois. The cholera epidemic was occurring against a backdrop of endemic malaria and typhoid fever, and high childhood morality.  In 1849-1850, “fevers” accounted for about 15% of all deaths and cholera for nearly 40% of all deaths.

As bad as the epidemic looks in the graph above, census taker Levi Sharp knows that it was actually far worse than the numbers suggest.

 

Mr Sharp reminds us of the problems with the federal mortality census. Relying on survivors, neighbors or next tenants will miss a lot of people. In an era when children were not mandated to attend school, it is likely that there were a fair number of children who few people knew existed, especially in rural areas.

The shape of the outbreak in St Clair county looks similar to the rest of the American Bottoms.

From a slide presentation I gave several years ago.

Cholera reached the American midwest as part of the second global pandemic. It came and went without people understanding the cause of the epidemic. It will still be a few years more until Dr John Snow discovers the link between cholera and water in 1854.