Parotitis is an inflammation of one or both parotid glands, the major salivary glands. While the inflammation may be bacterial in origin, parotitis is mostly the result of an infection with the mumps virus.
In January 2015, the Chicago Department of Public Health issued an alert to local doctors to test for both influenza and mumps, when diagnosing parotitis, as several unusual influenza-related cases had surfaced.
'Since December 2014, multiple states have notified CDC of laboratory-confirmed influenza infections in persons who have swelling of their salivary glands (a condition called ‘parotitis’). Of the cases of influenza infection with parotitis that have been reported to CDC, the majority have occurred in children with influenza A (H3) infection, and have resulted in mild illness.
Parotitis is not a common symptom of influenza infection, although cases of parotitis with influenza infection have been reported in the past.'
Then, in August 2015, Eurosurveillance reported that Influenza A(H3N2) virus was detected in several children with a clinical diagnosis of mumps, who were sampled between December 2014 and February 2015 in England. Sequence analysis of an A(H3N2) virus from a child with suspected mumps showed the virus was similar to other circulating A(H3N2) viruses detected in winter 2014/15, which were antigenically drifted from the A(H3N2) vaccine strain.
The question of whether this so-called 3C.2a A(H3N2) influenza virus strains have an unusual tissue distribution compared with other A(H3N2) viruses or whether a subset of children infected with any influenza strain experience parotitis remains to be determined.
 CDC: What You Should Know for the 2014-2015 Influenza Season. See here.
 Thompson et al: Detection of influenza A(H3N2) virus in children with suspected mumps during winter 2014/15 in England in Eurosurveillance – 2015