How Contagious is Ebola Compared to Other Viruses?

On September 28, 2014, Thomas Eric Duncan was admitted to the Texas Health Presbyterian Hospital in Dallas, Texas.  He became the first confirmed case of an Ebola infection in which the symptoms began while in the United States.  After being in critical condition throughout his hospitalization, Thomas Eric Duncan died from his Ebola infection on October 8, 2014.

On October 10, 2014, Nina Pham, a 26-year-old nurse, became the first Dallas healthcare worker to be diagnosed with Ebola.  On October 15, 2014, Amber Vinson, a 29 year-old nurse, became the second healthcare worker to be diagnosed with Ebola.  According to Dr. Tom Frieden, Director of the Centers for Disease Control and Prevention (CDC), both Pham and Vinson had “extensive contact” with Duncan on September 28-30, when Duncan had “extensive production of body fluids” such as vomit and diarrhea.

When working around Duncan, Nina Pham and Amber Vinson wore the following personal protective equipment (PPE): gown, gloves, mask, and shield.  In theory, this PPE should have provided complete protection from infection with the Ebola virus.  On October 13, 2014, Dr. Frieden told reporters that, in the case of Pham, a “breach in protocol” had occurred.  That same day, prior to developing symptoms, Ms. Vinson took Frontier Airlines flight 1143 from Cleveland to Dallas/Fort Worth.

When trained nurses wearing proper PPE can get infected with the Ebola virus, this begs the question, just how contagious is this Ebola virus?  National Public Radio distilled it down to a mathematical term called R0 or R-nought.  R0, the reproduction number, is the number of people who catch the disease from one sick person, on average, in an outbreak.

It is helpful to contrast measles with Ebola.  Measles, one of the most contagious viruses known to man, is transmitted through the air when an infected individual breathes, coughs, or sneezes; an individual infected with measles is contagious before he or she gets sick.  Ebola, on the other hand, is not transmitted through the air.  Ebola transmission requires direct contact (through broken skin or mucous membranes) with the blood, secretions, organs or other bodily fluids of the infected person or through direct contact with surfaces and materials (e.g. bedding, clothing) that have been contaminated with these fluids.  These bodily fluids do not pose a risk in the time period before the infected person actually develops symptoms.

So, measles is nine times more contagious than Ebola (18 people infected vs. 2 people infected).  However, an R0 of 2 is nothing to dismiss lightly.  An R0 of 2 means one person infects two people, who then infect four people, then eight, 16, 32, and so on.  The CDC and its affiliated healthcare partners are betting that they can prevent this exponential growth by taking the following measures:

  • The CDC has discouraged travel to the West African Ebola hot spot countries of Liberia, Guinea, and Sierra Leone.
  • Travelers from Liberia, Guinea, and Sierra Leone will be screened upon arrival in the United States at five major airports.
  • Close contacts of Ebola victims will be monitored closely; they will be quarantined at the first sign of symptoms.
  • The CDC is working to educate U.S. healthcare facilities about how to safely manage a patient with suspected Ebola virus disease.

Within hours of a confirmed Ebola case at any hospital in the United States, the CDC will send an expert Ebola response team.

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