Earlier this summer, some 6,000 guests to the New England Aquarium in Boston were informed they could have been exposed to measles because a 17-year-old volunteer was infected. Measles, a highly contagious disease, is spread via secretions from coughing or sneezing of infected people. The germs can stay in the air for 2 hours, the New York State department of health said. Preventive treatment for measles must be given within six days of exposure to be effective. That was too late for most of those visiting the aquarium, because most were informed June 4 for exposures that occurred May 19 and May 22. In the New England Aquarium case, there were no further cases but several employees who could have been infected and could not locate vaccination records were required to stay home, a spokesman said in an interview. In addition, the Boston Public Health Commission advised visitors to the aquarium on those days who may not be immune to measles to avoid "public activity" for 21 days. There have been more than 115 cases of measles reported in the United States so far, this year -- the highest number since 1996. In the last decade, the median number of cases each year has been only 56, the Centers for Disease Control and Prevention said. Some of the cases are due to exposure from traveling to Western Europe and Africa, but in May the Massachusetts department of public health said of the total year-to-date cases, two acquired the infection in Europe, but the rest did not travel outside of the United States and only two cases were linked to one another. "Baby boomers may remember getting the measles as a child, but the vast majority of today's parents and children have not seen a case of measles or chicken pox. They didn't experience it and can't understand the risks these infectious diseases have," said Dr. Andrew Bonwit, who specializes in pediatric infectious diseases at Loyola University Health System near Chicago. "Death from measles is rare, but it does occur, and there are many complications that can cause severe illness such as pneumonia and encephalitis." Among the other complications from measles are: a bacterial ear infection, bronchitis, laryngitis, croup and a low blood platelet count that interferes with blood clotting. Pregnant women who get measles can lose the baby, experience preterm labor or have a baby with low birth weight, the Mayo Clinic said. People born before Jan. 1, 1957, or who have a history of physician-diagnosed measles may be considered immune from the disease as are those who have received two doses of the measles-mumps-rubella vaccine, which was first used routinely in the early 1960s. Many may think measles in the United States was wiped out long ago and by the late 1990s, the number of cases was very low, but while states may require a long list of vaccinations children must have before starting school or even being in daycare, not all U.S. children are vaccinated. Some U.S. vaccination levels are as high as 95 percent in some places, the CDC said, but there are some regions where the number is much lower. Some children are home schooled and may not be vaccinated, some children may have chronic diseases that do not allow for vaccinations, newborns cannot be vaccinated until they are older, some are allergic, some have religious reasons and some parents just choose not to vaccinate children. "I worked a year in Angola and there no one chose to not vaccinate. They were clamoring for vaccinations because they were watching children die from measles, chicken pox," Dr. Jorge Parada, director of infection prevention and control at Loyola, said. "We have forgotten what infectious disease can do and many parents today ask, 'Do I really have to vaccinate my child?' The threat of these diseases persists and while parents may not be aware of all of the vaccines required, those in family care and pediatricians have the process down." Before the routine use of vaccinations, some 500 U.S. children died of measles each year and about 1,000 suffered permanent brain damage or deafness, the CDC said. Primary care physicians and pediatricians receive updated recommended immunization charts each year and many have the required documentation forms. Public schools are usually required to receive documentation on required vaccinations no later than one month after school starts, Parada said. "Parents need to remember that almost every one of the required or recommended vaccines come as a series of shots -- hepatitis A, hepatitis B, polio, measles, mumps, rubella and varicella -- to assure that the child builds sufficient immunity to the various infections," Bonwit said. "If a child falls behind the standard schedule, his or her pediatrician can plan a catch-up schedule based on standard recommendations." College students may also have to satisfy vaccination requirements. "The flu, meningitis and the human papilloma virus -- for women and men age 26 or younger, to prevent genital warts and cancer -- are important vaccinations for college-age adults," Parada said. Insurance coverage of recommended vaccinations varies by provider and plan level, but most required vaccinations for children and teens are covered by private and government health insurance. "Subsidized or even free vaccinations are available for those who qualify so there is no financial reason to not get vaccines," Parada advised. A chart on vaccinations and when to get them is at: www.cdc.gov/vaccines. Check with state and local health departments for clinics that offer those who qualify for free or subsidized vaccinations. "Many parents get in the rhythm of having their child vaccinated every few months as infants and even annually as a family for the flu," Parada said. "Getting regular shots for preventive medicine is a good life lesson to learn, right along with the alphabet and arithmetic."