Respiratory virus seasons usually follow a fairly well-known pattern. Enterovirus 68 (EV-D68) is a summer-to-early fall virus with biennial peak years. Rhinovirus (HRv) and adenovirus (Adv) occur nearly year-round but may have small upticks in the first month or so that children return to school. Early in the school year, upper respiratory infections from both HRv and Adv and viral sore throats from Adv are common, with conjunctivitis from Adv outbreaks in some years. October to November is human parainfluenza (HPiV) 1 and 2 season, often presenting as croup. Human metapneumovirus infections span October through April. In late November to December, influenza begins, usually with an A type, later transitioning to a B type in February through April. Also in December, respiratory syncytial virus (RSV) starts, characteristically with bronchiolitis presentations, peaking in February to March and tapering off in May. In late March to April, HPiV 3 also appears for 4-6 weeks.
Will 2020-2021 be different?
Summer was remarkably free of expected enterovirus activity, suggesting that the seasonal parade may differ this year. Remember that the 2019-2020 respiratory season suddenly and nearly completely stopped in March because of social distancing and lockdowns needed to address the SARS-CoV-2 pandemic.
The mild influenza season in the southern hemisphere suggests that our influenza season also could be mild. But perhaps not – most southern hemisphere countries that are surveyed for influenza activities had the most intense SARS-CoV-2 mitigations, making the observed mildness potentially related more to social mitigation than less virulent influenza strains. If so, southern hemisphere influenza data may not apply to the United States, where social distancing and masks are ignored or used inconsistently by almost half the population.
Further, the stop-and-go pattern of in-person school/college attendance adds to uncertainties for the usual orderly virus-specific seasonality. The result may be multiple stop-and-go “pop-up” or “mini” outbreaks for any given virus potentially reflected as exaggerated local or regional differences in circulation of various viruses. The erratic seasonality also would increase coinfections, which could present with more severe or different symptoms.
SARS-CoV-2’s potential interaction
Will the relatively mild presentations for most children with SARS-CoV-2 hold up in the setting of coinfections or sequential respiratory viral infections? Could SARS-CoV-2 cause worse/more prolonged symptoms or more sequelae if paired simultaneously or in tandem with a traditional respiratory virus? To date, data on the frequency and severity of SARS-CoV-2 coinfections are conflicting and sparse, but it appears that non-SARS-CoV-2 viruses can be involved in 15%-50% pediatric acute respiratory infections.1,2
However, it may not be important to know about coinfecting viruses other than influenza (can be treated) or SARS-CoV-2 (needs quarantine and contact tracing), unless symptoms are atypical or more severe than usual. For example, a young child with bronchiolitis is most likely infected with RSV, but HPiV, influenza, metapneumovirus, HRv, and even SARS-CoV-2 can cause bronchiolitis. Even so, testing outpatients for RSV or non-influenza is not routine or even clinically helpful. Supportive treatment and restriction from daycare attendance are sufficient management for outpatient ARIs whether presenting as bronchiolitis or not.