2 Seeking the Cause

Reading 2

Ebola and Measles: Identifying Patient Zero

In this reading students explore the first big idea of epidemiology, identifying the index case or Patient Zero, the first recorded case of a disease in an outbreak or epidemic.

Identifying patient zero in an epidemic is critical. By knowing where the disease first occurred, scientists may be able to identify the source of infection and prevent future outbreaks.

Who was patient zero in the Ebola epidemic and measles outbreak?
How did he get infected and how did it spread from him?

Students specifically look at how the first Ebola and measles cases were identified.

The first recorded case of a disease in an outbreak or epidemic is called patient zero or the index case.

Identifying patient zero in an epidemic is critical. By knowing where the disease first occurred, scientists may be able to identify the source of infection and prevent future outbreaks.

Who were patients zero in the Ebola epidemic and measles outbreak?
How did they get infected and how did it spread from them?

Patient Zero: Ebola

Ebola virus is a zoonotic virus, that is, a virus that normally resides in animals but can infect humans and cause disease. The spread of Ebola from animal to human in earlier outbreaks had been traced to hunters who captured and prepared fruit bats for food. But patient zero in the most recent 2014 epidemic of Ebola was believed to be a 2-year old boy living in a small village in Guinea. The toddler may have played near a tree infested with a species of bats believed to be reservoirs of the Ebola virus. Researchers are still unclear how the boy got infected. What is clear is the path the outbreak took once the virus had jumped from animal to human. Figure 2.1 shows how the virus moved from the 2-yearold boy and began its treacherous pathway of infection that resulted in 11,000 deaths in Guinea, Liberia, and Sierra Leone.

Figure 2.1 Pathway of Ebola infection from patient zero. From LiveScience.com.

Click on the image above to view an enlarged version.

Patient Zero: Measles

In December 2014, an 11 year old was admitted to the hospital with a rash. The unvaccinated child was diagnosed with measles believed to have been contracted during a visit to Disneyland. This case was patient zero, the first reported case of the 2015 measles outbreak in the United States. It is likely that the child was infected at the amusement park by a traveler who himself became infected overseas. However, no actual source has been identified. Between January 1, 2015 and January 2, 2016 189 individuals in 24 states cases of measles were reported, 60% of which were linked to patient zero in California (see Figure 2.2)

The year 2014 also saw a record number of measles with 667 in 27 states, the greatest number of cases since measles was considered eliminated from the United States in 2000. Patient in this outbreak was believed to be an Amish missionary returning from the Philippines. The cause of this upsurge in measles in recent years is most likely due to a rise in the number of unvaccinated Americans. Measles is still prevalent in many parts of the world including some countries in Europe, Asia, the Pacific, and Africa. Travelers who become infected abroad can initiate an outbreak when they return to a community where groups of individuals have not been vaccinated.

Figure 2.2 Measles cases in the U.S. in 2016. From cdc.gov.

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Additional Resources for Module 2 Reading 2

Patient Zero Hunt, Radio Lab

“The greatest mysteries have a shadowy figure at the center—someone who sets things in motion and holds the key to how the story unfolds. In epidemiology, this central character is known as Patient Zero—the case at the heart of an outbreak. This hour, Radiolab hunts for Patient Zeroes from all over the map.”

Patient Zero, WGBH.

A WGBH Video about patient believed to be patient zero in the Ebola outbreak in west Africa and how the disease spread from there.