Study Offers Insight into Epidemiology of MIS-C Cases

Older children seem to be at higher risk for myocarditis and pneumonia.

A new cross-sectional study has further elucidated the clinical, geographic, and temporal characteristics of cases related to multisystem inflammatory syndrome in children (MIS-C), a newly identified condition arising from the ongoing coronavirus disease 2019 (COVID-19) pandemic.

“Although most children with SARS-CoV-2 infection have mild or no symptoms, some children, particularly those with underlying conditions, can have severe illness,” the study investigators noted. “Clinical manifestations of hospitalized patients with COVID-19 may have some overlap with that of MIS-C.”

A team, led by Ermias Belay, MD, US Centers for Disease Control and Prevention Response Team, used clinical and laboratory data of patients diagnosed with MIS-C, which included cases of illness onset from March 2020-January 2021.

The geographical and temporal distributions of MIS-C were then compared with cases of COVID-19 at the national level and by region.

Highlights: Clinical Characteristics

The investigators identified a total of 1733 patients who met the clinical definition of MIS-C (and whose condition could not otherwise be explained).

Of this total, 57.6% were male, and 71.3% were Hispanic or non-Hispanic black.

The proportion of reported cases of gastrointestinal symptoms, rash, and conjunctival hyperemia ranged from 53% to 67% of patients. As many as 54% had hypotension or shock, and 58.2% of patients were admitted to the intensive care unit.

As for prevalence of cardiological complications, cardiac dysfunction was reported in 31.0% of patients, pericardial effusion in 23.4%, myocarditis in 17.3%, and coronary artery dilatation or aneurysms in 16.5%.

Children aged 0-4 years notably had the lowest proportion of severe manifestations. Nonetheless, of this cohort, 38.4% experienced hypotension or shock, and 44.3% were admitted for intensive care.

Patients 18-20 years old had the highest proportions of myocarditis (30.9%), pneumonia (36.4%), acute respiratory syndrome (18.2%), and polymerase chain reaction positivity (70.9%). This age group also had the greatest proportion of reported COVID-19-like illness (63%) prior to diagnosis of MIS-C.

Overall, the analysis found that a total of 24 (1.4%) patients had died from MIS-C.

Highlights: Geographic and Temporal Characteristics

The national MIS-C incidence per 100,000 persons younger than 21 years was 2.1, with a variance of 0.2-6.3 in states that reported cases.

“Patients with MIS-C from large central metro counties made up 57% of [all MIS-C ] patients up to June 30, which declined to 37% from July onwards,” the investigators noted. “The proportion of patients from small metro, micropolitan, or noncore areas increased from 6% to 18% over the 2 time periods.”

The burden of MIS-C for each state was generally highest in the Northeast, while the West and Midwest demonstrated high burdens of pediatric COVID-19.

Belay’s team also identified 3 peaks in MIS-C cases—which occurred in early May, early August, and December. The first 2 peaks followed the COVID-19 peaks by 2-5 weeks, while the third peak may seem to follow the same pattern.

Even more, the first MIS-C peak largely centered in the northeastern region, and the second peak in the south and west regions, findings that are consistent with the predominance of COVID-19 during those times.

Further, patients identified during the first peak were significantly more likely to experience cardiac dysfunction and myocarditis, an observation that has yet to be fully understood.

“As the COVID-19 pandemic spreads, causing a third peak and more sustained transmission across the United States, physicians should maintain a high index of suspicion for MIS-C to promptly diagnose and treat these patients,” the investigators wrote.

"Practitioners should report patients suspected with MIS-C to local and state health departments,” they concluded.

The study, "Trends in Geographic and Temporal Distribution of US Children With Multisystem Inflammatory Syndrome During the COVID-19 Pandemic," was published online in JAMA Pediatrics.