This article, written by Dr. Shamard Charles, originally appeared on NBC News
A cruise ship was quarantined Tuesday in Saint Lucia after the island nation’s chief medical officer cited concerns that crew members and passengers possibly infected with measles might spread the highly contagious virus, causing an outbreak.
“One infected person can easily infect others through coughing, sneezing, droplets being on various surfaces, etc. So because of the risk of potential infection—not just from the confirmed measles case but from other persons who may be on the boat at the time—we thought it prudent not to allow anyone to disembark,” Dr. Merelene Fredericks-James said in a statement.
Quarantines are one of many measures used by public health officials to limit the spread of disease, especially to vulnerable populations, such as pregnant women, unvaccinated children, and those with weak immune systems.
WHAT IS A MEDICAL QUARANTINE?
According to the Centers for Disease Control and Prevention, a quarantine separates and restricts the movement of people who were exposed to a contagious disease to see if they become sick. This is different than isolation in which sick people are identified and separated from people who are not sick.
“Isolation is used to separate ill persons who have a communicable disease from those who are healthy. The most important thing is that a distance is created between the respiratory secretions of the infected person and others.
The person on the cruise ship has to stay in their room and not come into contact with others, especially those who are not vaccinated,” said Dr. Mirella Salvatore, a travel medicine and infectious diseases expert at Weill Cornell Medicine and New York-Presbyterian.
“Quarantine is used to separate and restrict the movement of well persons who may have been exposed to a communicable disease to see if they become ill. These people may have been exposed to a disease and do not know it, or they may have the disease but do not show symptoms,” she continued.
Quarantines can take different forms depending on the environment. In the case of the cruise ship, the person was isolated from the rest of the group and the boat was quarantined, or cleared from people who were not on the boat since it now carried the disease which can live on surfaces for up to two hours.
While health officials figure out who is and who isn’t infected, they prepare post-exposure prophylactic medicines, such as the measles, mumps and rubella vaccine or immunoglobulin, to protect those who are at the highest risk of exposure from developing the disease. “This is a way to try to prevent measles after you’ve come into contact with the virus,” Salvatore told NBC News.
Quarantine times vary, but typically last for at least 21 days — the typical the time from the moment of measles exposure to the time when signs and symptoms of the disease disappear — or until public health officials can prove that everyone is immune and safe.
WHAT DOES A QUARANTINE LOOK LIKE?
The United States is in the midst of the worst measles outbreak — 704 cases across 22 states according to the latest data reported by the CDC — since measles was declared eliminated in 2000.
Most recently, quarantines have been used at California State University, Los Angeles and the University of California, Los Angeles to limit measles exposure of more than 800 students. Members of the university were cleared after providing proof of receiving 2 doses of the MMR vaccine. If students could not provide complete vaccination records, they were kept away from classes until blood test results proved the virus was not in their system.
WHEN IS A QUARANTINE LIFTED?
Measles stays in the air for 1 to 2 hours even when someone isn’t in the room and it’s contagious before someone gets the rash and 4 days after the rash is gone, so a quarantine is often longer than a simple isolation, Salvatore said.
In order for the quarantine to be lifted, public health officials have to prove that the exposure is eliminated. One way is to ask for vaccination records; the other way is to do tests that confirm that those who were exposed don’t have the disease.
There are only two ways to be protected against measles: One is to have been naturally infected with the disease, which then gives you a specific immune response, and the other is to be vaccinated.
Those born before 1957 are likely to have been exposed to measles, even if it was a very mild “subclinical” infection that produced no symptoms, and are therefore likely to be immune for life.
Those born between 1957 and 1989 likely received one shot — and sometimes a weakened version if they received the shot between 1957 and 1962 — and may require a booster shot or be required to provide proof that they received 2 vaccine shots.
Many people do not remember getting the shot or don’t have access to old medical records. Salvatore encourages those who are unsure of their vaccination status to get a booster shot if they are worried.
“For whoever feels they are not immunized, there is no danger in getting a booster shot although it is important to note that those who are pregnant or immunocompromised should speak to their doctor as the MMR vaccine is a live vaccine and can cause the disease in those populations.”
Dr. Shamard Charles is a physician-journalist for NBC News and Today, reporting on health policy, public health initiatives, diversity in medicine, and new developments in health care research and medical treatments.