Acute viral parotitis is an infectious disease usually caused by the mumps virus (genus Rubulaviris, Paramyxoviridae family) characterized by fever and swelling and tenderness of one or more salivary glands. However, in rare cases, it may be caused by other viruses (adenovirus, enterovirus, Epstein-Barr virus, human herpesvirus 6). During the 2014–2015 influenza season in the United States, there were 256 reported cases of parotitis associated with circulating influenza A viruses (H3N2) (Orthomyxoviridae family). Most patients presented with the classic symptoms, pain and facial and gland swelling, and were considered cases of winter parotitis (parotitis occurring during the influenza season that may not be caused by the mumps virus).1 Later studies conducted in other countries demonstrated the association between the influenza A (H3N2) and parotitis cases negative for the mumps virus.2–4 These data motivated us to conduct an observational study, as we had not suspected winter parotitis in previous seasons.

In the 2025–2026 season, mumps was suspected in eight pediatric patients based on the clinical presentation. Samples of saliva or oral swabs were initially tested with a PCR panel to screen for mumps virus (Allplex meningitis panel assay, Seegene, South Korea), and, if the results were negative, with a differential multiplex respiratory virus panel (Allplex Respiratory Assay, Seegene, South Korea). We collected clinical data from the laboratory test orders that accompanied the samples.

All eight samples from patients with suspected mumps tested negative for mumps virus, and 5 (62.5%) tested positive for influenza A (H3N2) subclade K (J.2.4.1). The mean age of the patients was 6.2 years, and 60% were male. In 80% of patients, the involved gland was the right parotid gland. The most frequent respiratory symptom in the sample was coughing, and influenza was not considered at the time of diagnosis. Table 1 presents the main characteristics of the patients with parotitis associated with influenza virus infection. All had been correctly vaccinated against mumps with the recommended two doses of vaccine (measles, mumps, rubella vaccine), but had not been vaccinated against influenza; they received symptomatic treatment with ibuprofen, and none experienced complications (save for one case of reactive lymphadenopathy) or sequelae.

In a similar pattern to the one observed in the United States, Canada also reported that in the 2014–2015 season, 13% of cases of parotitis that tested negative for mumps were associated with the presence of influenza A (H3N2) clade 3C.2a, which was the main circulating influenza virus in that season,4 while the United Kingdom reported a proportion of 15% out of the 107 suspected cases of mumps.5 What remains unclear is whether this influenza subtype specifically affects the epithelial cells of the parotid glands. It has been proposed that parotitis may result from either viral replication in the salivary epithelium or bacterial superinfection of the parotid.4,5 In fact, influenza A virus (H3N2) has been detected in the salivary glands in an experimental murine model of influenza infection. This finding suggests that influenza viruses can replicate in these glands and cause local inflammation.1,4

A case-control study found a significant association between this type of parotitis and male sex, despite the absence of known anatomical differences in the parotid glands between the sexes4; our findings confirmed the predominance of the male sex. Although our study included a small number of tested samples, influenza A (H3N2) was detected in 62.5% of cases, a percentage similar to the 70% reported in the Argentinean study.2 A study conducted by Centrone et al.3 in Italy in the past influenza season (2024–2025) included 16 cases of parotitis, of which 87.5% were associated with influenza A (H3N2) clade 2a.3a.1 viruses, which were circulating that season.

In light of the findings of these studies, there seems to be a clear sporadic association between parotitis and influenza, in particular with influenza A (H3N2) and the predominant clade in the corresponding influenza season. When a child who is correctly vaccinated against mumps presents with parotitis during the flu season and has negative PCR results for the mumps virus, influenza-associated winter parotitis should be suspected, especially if influenza A (H3N2) is the predominant circulating subtype.6 Larger multicenter studies are required to confirm these findings.