A mumps outbreak is linked to D'Jais Bar and Grill in Belmar, N.J., health officials said.

Health officials are investigating an outbreak of mumps linked to a bar on the Jersey Shore.

At least 21 people are thought to have contracted the contagious disease after visiting D'Jais Bar and Grill in Belmar, N.J., according to the Monmouth County Health Department.

"The medical professionals advised these individuals to be on bed rest, increase their fluid intake and take steps to reduce their fever," the county's public health coordinator Michael Meddis said in a statement.

The outbreak was first reported Wednesday after seven people developed symptoms of mumps, which include fever, fatigue, head and muscle aches, and swollen salivary glands under the ears. Since then, another 15 people have come forward with symptoms, health officials said in a statement Thursday.

One of the 22 people infected is a pre-schooler with no reported connection to D'Jais Bar.

The mumps virus spreads through tiny droplets of saliva or mucus, according to the U.S. Centers for Disease Control and Prevention. And because up to 50 percent of people with mumps have mild symptoms or none at all, many people fail to realize they're contagious.

"Most mumps transmission likely occurs before the salivary glands begin to swell and within the five days after the swelling begins," the CDC says on its website .

A vaccine against measles, mumps and rubella, known as the MMR vaccine, can reduce the risk of infection by up to 88 percent, according to the CDC. The vaccine is given in two doses - one in babies 12 to 15 months old and one in children aged 4 to 6.

Most people infected with the virus recover, according to the CDC. But mumps can lead to dangerous complications, including inflammation of the brain, testicles, ovaries and breasts.

The CDC recommends the following precautions for people with mumps:

• Minimize close contact with other people, especially those with weakened immune systems;
• Stay home from work or school for five days after your glands begin to swell;
• Cover your mouth and nose with a tissue or your sleeve when you cough or sneeze;
• Wash hands thoroughly and frequently with soap;
• Don't share drinks or utensils;
• Keep frequently touched surfaces clean with soap and water.