METHODS: The California Department of Public Health (CDPH) investigated influenza-associated rash by performing influenza rRT-PCR testing on archived measles negative respiratory specimens submitted for measles testing during the peak 2013-2014 and 2014-2015 influenza seasons. Medical records, CDPH surveillance data, and specimen submission forms were used to assess patient rash and other clinical data. For 2014-2015 patients, we compared demographic and clinical characteristics among patients who were measles negative/influenza positive to those who were measles negative/influenza negative and to those who were measles positive and not tested for influenza.
RESULTS: Of 33 2013-2014 patients, 1 (3%) tested positive for influenza B (Victoria lineage). Among the 190 2014-2015 patients, 30 (16%) were influenza positive; 25 influenza A H3N2 and 5 influenza B (4 Yamagata lineage, 1 Victoria lineage). The median age of influenza positive patients in 2014-2015 was 7.5 years compared to 2.8 years for influenza negative patients (p=0.02) and 22.0 years for measles cases (p<0.001). Influenza positive patients had a longer, but not statistically significant, mean duration of fever to rash onset compared to influenza negative patients and measles cases (3.8 days vs 2.7 days vs 3.1 days, respectively). Influenza positive patients were less likely to first note rash on their face (50% vs 92%; p<0.001), have a descending rash (50% vs 90%; p<0.001), or have conjunctivitis (26% vs 54%; p=0.03) compared to measles cases. No influenza positive rash patients were hospitalized, compared with 14/93 (15%) of measles cases (p <0.001).
CONCLUSIONS: Influenza infection may be associated with rash. In contrast to previous reports, rash may be associated with both influenza A H3N2 and influenza B viruses. In California, influenza-associated rash was more common during the 2014-2015 influenza season and occurred primarily among young children. However, this result may be due in part to increased measles testing secondary to the 2015 Disneyland measles outbreak and differences in the predominant influenza A strain. Patients with influenza-associated rash were less likely to have classic measles symptoms. Providers should consider influenza in addition to measles in patients with cough, fever and morbilliform rash during periods of elevated influenza activity.