The COVID-19 virus is starting to rise just as students in the metro Denver area head back to school.

Denver Public Schools (DPS) is one of the last school districts to start with Monday the first day of classes for most campuses.

“We are seeing increases in emergency department visits and the percent positivity, as well,” said Alicia Cronquis, COVID-19 surveillance program manager for the state health department. “We track COVID a bunch of different ways.”

The Colorado Department of Public Health and Environment tracks COVID-19 trends through three streams of data: wastewater, emergency-department visits, and laboratory testing. Because people shed the virus before symptoms, wastewater is an early signal. Partnering with utilities statewide, recent readings — from Colorado Springs to Greeley — show a steady rise in community transmission, officials said.

Visits to the emergency room across the state show COVID-19 illnesses climbing from 0.17% in early June to 0.61% by Aug. 9, state data shows.

Over the same time period, positive lab tests rose from 3.8% to 10.4%.

Hospitalizations — for all the common respiratory diseases: COVID-19, flu and RSV — have remained steady or dipped slightly. Hospital admissions typically lag one-to-two weeks behind emergency room and urgent care visits, as the most severe cases peak later.

This comes as more than 85,000 students return to classrooms and other congregate settings — buses, cafeterias, gyms and locker rooms — where respiratory viruses spread easily.

With the exception of COVID-19 (a relatively new disease that has not yet developed a firm pattern), the other respiratory diseases — RSV and the flu — normally behave seasonally. Both RSV and influenza cases usually start up in October and peak in November and December, although the flu can linger into March and April.

RSV is a common respiratory disease that can be serious for the very young and old. About 90% of those hospitalized with RSV were children.

A vaccine is available for all three diseases.

Since October, Colorado has seen nine pediatric deaths, three in each: RSV, flu and COVID-19, state data shows.

“While we aren’t seeing huge numbers in patients coming in with respiratory illnesses, we have seen incremental increases in patients with COVID-19 and anticipate patients experiencing respiratory illness to increase as kids return to school,” Dr. Samuel Dominguez, pediatric infectious disease expert at Children’s Hospital Colorado, told The Denver Gazette.

“Children’s Hospital Colorado encourages all caregivers to learn more about immunizations for flu, RSV and COVID-19 as kids head back to school and ahead of the respiratory season.”