Newswise — Measles have reached a 20-year high in the United States and the cause lies squarely with those who deliberately refuse to be vaccinated.

Eighty-five percent of the unvaccinated U.S. residents who contracted measles cited religious, philosophical or personal reasons for not getting immunized, according to the Center for Disease Control. “Religious, philosophical or personal reasons are not medical reasons for not getting vaccinated,” says Jorge Parada, MD, medical director, infectious disease at Loyola University Health System.

Between January 1 and May 23 of 2014, 288 measles cases were reported to the federal health agency, the highest year-to-date total since 1994. Nationwide, measles has caused 43 patients to be hospitalized this year but no deaths have occurred.

“Whether they recognize it or not, most people who consciously opt out of vaccines are depending on herd immunity – that enough other people will get vaccinated so as to prevent widespread infection – yet by opting out they are seriously undermining the very herd immunity they depend on for safety,” says Dr. Parada. “It’s a numbers game, and America is losing ground in the fight against preventable disease.” Parada says the people he fears for most are those who for legitimate medical reasons, cannot tolerate a vaccine. “Herd immunity may be life-saving for people who medically cannot tolerate a vaccine for these people are the most vulnerable to disease,” says Dr. Parada. “It should be frightening to every single American that people deliberately are refusing vaccinations.”

Too often the people who consciously opt out of vaccinations do so counting on not getting sick, says Dr. Parada. “I have worked in Africa and Europe where I witnessed outbreaks of vaccine-preventable illness due to lack of access to immunizations, not due to personal choice,” he says. “I saw moms begging for vaccines for their kids. In America, the collective memory of the horrific outbreaks of preventable diseases has faded. ”

Many simply underestimate the risk of natural infection and overestimate the risk of vaccinations. “Deliberately choosing not to get vaccinated while relying that others will get vaccinated is a dangerous combination,” says Dr. Parada. “I only hope those who opt out do not come to discover firsthand the potentially devastating consequences of natural infection.”

Loyola University Health System is recognized internationally as a leader in infection control and prevention. Loyola is one of a few select hospitals who invest in universal screening of all inpatients for MRSA. Loyola was one of the first institutions to require all staff to have mandatory flu shots as a condition of employment. Loyola also actively screens emergency department patients for HIV/AIDS as part of an ongoing research study