Each dot represents one case of mumps between late June 2009 and late June 2010. The New England Journal of Medicine hide caption

itoggle caption The New England Journal of Medicine

Two boys study together at a Chicago yeshiva in 2009. Public health officials say this type of close physical contact caused a mumps outbreak to spread throughout several orthodox Jewish communities in and around New York City. M. Spencer Green/AP hide caption

itoggle caption M. Spencer Green/AP