Why not? According to Jessica Bralish, the state health department's director of communications, positive tests must be "epidemiologically linked" — and the math determining whether that's happened can get tricky.
The CDPHE's current standard for outbreaks differs by setting. For residential health-care and correctional facilities, the department must confirm two or more COVID-19 cases among residents, staffers, attendees and other people connected to a specific place within a fourteen-day period — the definition put in place on a universal basis during the first weeks of the pandemic. But since June 1, at least five confirmed or probable cases of COVID-19 in a fourteen-day period must be identified at all other locations, including K-12 schools, before an outbreak is designated.
Five isn't necessarily a magic number, however, as demonstrated by schools listed on the Douglas County School District's interactive COVID-19 case tracker. Four DCSD schools experienced five or more confirmed COVID cases from October 12 to October 17, the most recent dates available: Castle View High School and Northeast Elementary, with six each, and Highlands Ranch High School and Flagstone Elementary, with five apiece. But while Highlands Ranch High School and Northeast Elementary both made the CDPHE's most recent outbreaks roster, posted on October 20, neither Castle View High School nor Flagstone Elementary appear.
Why not? Speaking generally, Bralish notes that "schools may have multiple individuals infected with COVID-19 at the same time without meeting the outbreak definition if cases are not 'epidemiologically linked.'"
This last term is defined by the federal Centers for Disease Control and Prevention as "a case in which the patient has/has had contact with one or more persons who have/had the disease, and transmission of the agent by the usual modes of transmission is plausible. A case may be considered epidemiologically linked to a laboratory-confirmed case if at least one case in the chain of transmission is laboratory-confirmed."
In other words, CDPHE contact tracers must definitively connect five cases to each other in order for a site to be deemed an outbreak. But if a student or staff member at a school hasn't had contact with anyone else at the facility who was infected, investigators will conclude that the individual caught the disease somewhere else — and that case wouldn't be included in the outbreak determination total.
According to various sources, cooperation with the CDPHE in terms of COVID reporting and contact tracing varies widely from school to school, with some institutions doing a stellar job of sharing the news and others doing everything in their power to avoid being deemed an outbreak. Bralish doesn't weigh in on this subject, but she encourages "schools to follow our school guidance to minimize disease transmission and to sign up for our school testing program, which can help ensure students continue in-person learning and minimize disease transmission.
She adds, "Schools are required to report individual cases to public health, and suspected and confirmed outbreaks must be reported within four hours."
That math isn't tricky at all.