Ebola Information
Ebola: Basics About the Disease
In March 2014, global health officials recognized an outbreak of Ebola virus disease (EVD) in Guinea, West Africa. In retrospect, officials determined that the outbreak began in December 2013, and spread to the adjacent countries of Liberia and Sierra Leone. In September 2014, the U.S. Centers for Disease Control and Prevention (CDC) confirmed the first EVD case diagnosed in the United States, heightening concerns among some who fear the disease could spread in American communities.
During an outbreak, EVD spreads through human-to-human transmission. Transmission requires direct contact with body fluids from an infected person or contaminated objects such as medical equipment. It cannot be spread through the air. Hence, EVD is not as easily transmitted as influenza or common cold viruses, which can be spread through the air. However, healthcare workers, family members, and others who care for EVD patients have a high risk of infection because they are in regular contact with infected body fluids.
In humans EVD has an incubation period—the time between exposure and onset of symptoms—from 2 to 21 days, with an average of 8 to10 days. Individuals are not contagious, meaning they cannot transmit EVD to others, until symptoms are present. Those surviving infection may still have Ebola virus in their bodies and remain contagious for several months after infection, even when symptoms are no longer present. They can be tested for the presence of virus in order to maintain their quarantine until they are no longer contagious.
Several laboratory tests are available to test patients for EVD. These tests may yield negative results within the first few days after symptoms appear. As a result, patients who have potentially been exposed to EVD and who show some of the symptoms above should be isolated, even if test results are negative, and retested a few days later.
The early symptoms of EVD are shared by many more common illnesses, complicating diagnosis. Symptoms may include a high fever (greater than 38.6°C, or 101.5°F), severe headache, muscle pain, weakness, diarrhea, vomiting, abdominal (stomach) pain, and unexplained hemorrhage (bleeding or bruising).
Death Rates
EVD is known and widely feared for being exceptionally deadly. The case fatality rate (CFR), the percentage of infected individuals who do not survive, generally exceeds 50%, an extraordinarily high rate among infectious diseases. The true CFR is an inherent property of the infectious agent (in this case, the Ebola Zaire virus). However, the measured CFR is affected by the availability of vaccines and specific treatments, as well as general medical care, among other factors. Perhaps the most significant factor is how cases are counted; whether counts are limited, for example, to cases in which EVD is confirmed with a laboratory test, or to hospitalized patients, or to patients for whom an outcome (lived or died) is confirmed. Different approaches to case counting can affect the measured CFR considerably.
WHO analyzed CFRs for the current outbreak in West Africa, limiting its analysis to patients with confirmed outcomes. It found rates of about 70% in each of the severely affected countries—Guinea (70.7%), Liberia (72.3%), and Sierra Leone (69.0%). In all three countries, hospitalized patients in this group had somewhat lower CFRs (ranging from 61% to 67%) than patients who were not hospitalized. Regardless of variations in measured rates, EVD is clearly a deadly disease.
Preventing Transmission
Prevention of human-to-human transmission of Ebola virus requires avoiding contact with body fluids of those who are sick. As a result, EVD is not likely to be easily transmitted in community settings in the United States. However, caregivers, including family members and healthcare workers, face considerable risk of transmission. Barrier protections (called personal protective equipment or PPE), liberal disinfection of premises and facilities housing EVD patients, and careful handling of human remains and contaminated objects are essential. In resource-constrained environments (such as in developing countries), consistent adherence to these practices can be hampered by shortages of personnel and supplies, and other factors. However, according to CDC, "virtually any hospital in the [United States] can do isolation for Ebola."
This information was provided from the CRS Report: Ebola: Basics About the Disease.
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