(RxWiki News) Measles is rare in the US but not completely gone, as recent exposures in Texas and Boston have demonstrated. So just how many cases has the US seen this year and where are they coming from?
To explore these questions, a team of researchers from the Centers for Disease Control and Prevention (CDC) analyzed measles cases reported so far in 2013 and found that case numbers this year have been high.
This new study shows that most of the measles cases were linked to exposures outside the US, and most occurred in unvaccinated people.
"Ask your doctor about your vaccination status."
Measles is a respiratory disease that is highly contagious and spread through the air, often when an infected person coughs or sneezes. Fever, cough, runny nose and a rash are common symptoms, but the disease can cause complications. The CDC estimates that around one or two out of 1,000 childhood cases result in death.
According to the authors of the new study, "measles elimination" was declared in the US in the year 2000, but measles cases still occur. Typically these cases can be traced back to an "imported" case — a person who was exposed to measles outside of the US.
During the years 2001 to 2012, the average annual number of measles cases in the US was 60 per year, including 26 imported cases, the study reported.
The years with the highest number of cases since the year 2000 occurred in the years 2008, which saw 140 measles cases, and 2001, which saw 220.
This study, led by Gregory Wallace, MD, of the CDC's National Center for Immunization and Respiratory Diseases, provided an update of measles counts by looking at cases reported to the CDC between January 1 and August 24, 2013.
During this time, 159 cases were reported from 16 different states and New York City. The age of patients ranged from zero days to 61 years. Eighteen patients (11 percent) were less than 1 year old, 40 (25 percent) were between the ages of 1 and 4 years old, 58 (36 percent) were between the ages of 5 and 19 years old and 43 (27 percent) were 20 years old or older.
In 2013, 17 patients (11 percent) required hospitalization. Four of these patients developed pneumonia. Zero deaths occurred.
People who were unvaccinated accounted for 131 of the patients (82 percent) and an additional 15 patients (9 percent) had an unknown vaccination status.
Of the 2013 cases, 42 (26 percent) were imported from another part of the world. Half of these imported cases (21 cases) came from the World Health Organization's European Region.
US residents returning from travel accounted for 23 of the imported cases, while visitors to the US made up 19 cases.
"Import-associated" cases (meaning imported cases and the people who developed measles after being exposed to an imported case in the US) made up the majority of measles cases during 2013 — 157 cases, or 99 percent. The two additional cases had an unknown source.
Eight outbreaks (three or more linked cases) have been seen in 2013, accounting for 77 percent of this year's cases. One of the outbreaks involved 58 cases in New York City, which the study authors noted was the biggest US outbreak since 1996.
"These outbreaks demonstrate that unvaccinated persons place themselves and their communities at risk for measles and that high vaccination coverage is important to prevent the spread of measles after importation," the study authors concluded.
Dr. Wallace and colleagues also highlighted the fact that though measles elimination is steady in the US, 20 million cases still occur around the globe each year.
"The increase in measles cases in the United States in 2013 serves as a reminder that imported measles cases can result in large outbreaks, particularly if introduced into areas with pockets of unvaccinated persons," Dr. Wallace and colleagues wrote.
This study was published September 12 in the CDC's Morbidity and Mortality Weekly Report (MMWR). No conflicts of interest were reported.