Cambridge Public Health staff does intake at an Oct. 16 flu and Covid vaccination clinic at the King Open School. (Photo: Cambridge Public Health Department)

For almost the entire pandemic, Asian residents of Cambridge have had the lowest Covid-19 case rate of any racial or ethnic group. That’s changed in the past two months, as cases per 100,000 population among Asians have crept up to outrank every other group except residents in the “other” category, a relatively small mix of racial groups.

For the week of April 17, the case rate for Asian residents was 61.4 cases per 100,000 population in that racial group. The closest to that number was 41.2 cases per 100,000 among Hispanic residents. Asian residents’ case rate dropped slightly lower than Hispanic residents’ rate in the next week, but aside from that, the rate among Asian residents has topped all groups except the “other” category since Feb. 27, according to figures posted by the city.

It’s not clear why, and Dawn Baxter, a spokesperson for the Cambridge Public Health Department, said the figures may not represent real differences in the risk of infection faced by different racial and ethnic groups in the city.

Increasing use of home tests means “we are working with more limited data,” Baxter said in an email. “At this point, it is often not possible to know if the fluctuations we see are the result of an actual trend in the community or the result of certain individuals or groups seeking PCR testing versus testing at home.”

Baxter said “a more detailed look at age-adjusted case rates among racial and ethnic groups over the past month shows relatively small differences across the demographic groups” and the health department is “not seeing anything overly concerning in terms of racial/ethnic fluctuations.”

Health officials continue to be concerned about rising cases, particularly in residents from 18 to 22 years old, Baxter said. That demographic is “highly tested” because colleges and universities have mandated regular, repeated Covid-19 tests for students and others on campus, but that changed in the past month; testing is now optional at the Massachusetts Institute of Technology, and Harvard will end testing mandates for all students and staff May 10, The Harvard Crimson reported.

Hispanics once led rate

Reinforcing the worry about increasing cases, Cambridge reported 264 new infections on Thursday, including 123 in residents in their 20s. Data on case rates among different racial and ethnic groups wasn’t updated.

Early in the pandemic, former Cambridge chief public health officer Claude Jacob used the case rates among racial and ethnic groups to expose the higher risks facing black residents. They had three times the case rate of white residents, and the health department targeted testing and education efforts to the black community.

It wasn’t long before Hispanic residents exceeded the case rate among black residents, but health officials did not give specifics about a response. The infection rate among Hispanic residents has remained higher than the rate among black residents except for the omicron surge in December and January.

Now there are other anomalies. For example, the case rate for black residents barely exceeded the rate for white residents in the most recent city report, for the week of April 24, perhaps because of the city’s efforts and community work. Eighty-four percent of black residents are fully vaccinated, although only 41 percent have received a booster.

Lack of demographic information

The city was one of the first during the pandemic to report cases and case rates among racial and ethnic groups to identify disparities and to target public health efforts. The health department goes further than many other health agencies to gather the information, asking residents for it when workers call people who have tested positive. At this point, case investigators are trying to contact everyone over 70 and family members of those under 5, sometimes expanding to residents over 60 and under 16, Baxter said.

Still, the cumulative proportion of Cambridge cases with no demographic information stood at 17.2 percent on Thursday and has exceeded 17 percent since April 1. That adds to the uncertainty about the number of infections in general, with less testing and unknown results from home antigen tests. Baxter said that “while we do have the race/ethnicity information for over 80 percent of reported cases, we are mindful that the reported data are increasingly less reflective of the complete picture of positive cases in Cambridge.”

As for the “other” category, it includes residents of more than one race, plus American Indians and native Alaskans, and Pacific Islanders and Hawaiians, Baxter said. Except for the mixed-race residents, the other categories are so small that health officials combined them so that individuals could not be identified, she said.

There are 4,433 individuals in the “other” category, which makes it the smallest racial or ethnic group in the city. That means that a few new cases can swell the case rate, since the rate is defined as the number of cases per 100,000 population of that racial group.