Los Altos High School saw a string of COVID-19 cases crop up last week, although no in-school transmission had been confirmed as of Tuesday morning, Nov. 9.

Five coronavirus cases were identified at Los Altos High School last week, plus another two at Alta Vista High and one at Mountain View High. In total, six students and two staff members tested positive for the coronavirus across the Mountain View Los Altos Union High School District.

That marks a "very significant uptick" in the number of cases in the district, compared to recent weeks, Associate Superintendent Leyla Benson said. Across the prior six weeks, only one student and one staff member had tested positive districtwide.

"This (increase) was really quite surprising to us and very concerning," said Benson, who is spearheading the district's response to COVID-19 cases. "We've spent a lot of time on it, trying to really look into it."

Although the district has been actively monitoring the situation and looking for connections between cases that might point to on-campus transmission, none has been identified to date.

"There is no specific in-school spread detected between the cases," Benson said. "In each one of the cases, there was a wide variety of circumstances, none of which closely aligned."

Out of all the cases, only two students shared a single class period and no one else in that class has tested positive, Benson said. The district has also looked into whether Los Altos High's homecoming festivities, including the Oct. 30 dance, could have led to the cases, but Benson said no connection has been made.

The two cases at Alta Vista posed a high likelihood of a connection, given the small size of the alternative school, which has roughly 60 students, but Benson said there were non-school activities that helped explain those cases. Los Altos and Mountain View high schools each have over 2,000 students.

It appears that a "confluence of circumstances" is driving the recent increase in cases in the district, Benson said, including gatherings and family events, travel and students participating in more activities outside of school.

At the same time, Benson cautioned that on-campus transmission could still be identified as test results come back from those who were in contact with the positive cases.

It is also impossible to know with certainty the origin of each case, Benson said, adding that the more activities someone participates in, the harder it is to determine the source of their infection.

Procedures for positive cases

Whenever someone tests positive for COVID-19, the school district sends a notification letter to everyone determined to be a close contact. That includes every student who shares a class with the positive case, Benson said. Because high schoolers switch between multiple periods each day, a single infected person can often result in over 100 close contact notifications.

Last week alone, the eight cases resulted in 975 close contact notifications. Some students may have received multiple exposure letters about separate cases.

All close contacts are required to get tested for COVID-19, Benson said. Whether they can remain in school or need to quarantine is governed by a complex "decision tree" from Santa Clara County, which includes factors such as whether the close contact has symptoms, is vaccinated and wore a mask during the exposure.

According to Benson, most of those who have tested positive so far are vaccinated and thus have had less severe reactions to the virus.

She stressed the importance of vaccination, including getting a booster dose if eligible, as well as frequent COVID-19 testing. The district is also encouraging, though not requiring, wearing a mask outdoors if in close proximity to others. No one should come to school if they feel any symptoms, Benson said.

"We understand that people are going to engage in social activities, that's happening right now," Benson said. "If we test on a regular basis, then people who are positive can remove themselves, so that keeps our school a safer place."