A recently released map from the U.S. Centers for Disease Control and Prevention (CDC) shows areas across the country that saw a spike in COVID-19 cases over Thanksgiving.

In the week ending Nov. 30, four percent of cases statewide were positive, down from 4.5 percent the previous week.

California, Arizona, Hawaii and Nevada had the highest percentage of positive tests, with 7.1 percent of tests in the week ending November 30.

Meanwhile, Wyoming, Utah, South Dakota, North Dakota, Montana and Colorado had a 6.3 percent positivity rate.

Nebraska, Missouri, Kansas and Iowa all had a positivity rate of 5.2 percent. In all other states, fewer than 5 percent of tests came back positive.

Texas, Oklahoma, New Mexico, Louisiana and Arkansas had the lowest positivity rate, with only 1.7 percent of tests coming back positive.

COVID-19 nucleic acid amplification tests (NAATs), like PCR tests, detect the virus’s genetic material to determine whether someone is infected. The sample is first treated to extract the virus’s RNA, which is then converted into DNA using a special enzyme.

Many copies of a specific part of the virus’s DNA are then created using a process called amplification, which makes it easier to detect even tiny amounts of the virus. When the copies are made, a special dye lights up in the presence of the virus, signaling a positive result.

Nationally, CDC data shows that 0.6 percent of emergency room visits nationwide during Thanksgiving week were related to COVID-19, a 0.1 percent increase from the week before. Although New Mexico had one of the lowest positivity rates, it had the highest percentage of emergency room visits related to COVID-19 at 2 percent. Arizona followed with 1.7 percent, while 1.1 percent of emergency room visits in South Dakota and Colorado were related to COVID-19. In all other states, less than 1 percent of emergency room visits were COVID-related.

Meanwhile, there were 179 COVID-19 deaths statewide in the week ending Nov. 30, compared to 297 the week before and 453 deaths in the week ending Nov. 16.

This came after “very high” levels of the SARS-CoV-2 virus were detected in wastewater in Idaho, New Mexico and South Dakota between November 17th and 23rd.

The week before, between November 10th and 16th, this level of virus was only present in New Mexico wastewater. Currently, only New Mexico has very high levels of SARS-CoV-2 in wastewater.

The CDC is monitoring COVID-19 levels in wastewater as part of its surveillance strategy to track the spread of the virus in communities. Infected people shed the virus in their feces, meaning wastewater monitoring can detect increases in infection rates sooner than clinical testing or hospitalization.

“Virus activity in wastewater indicates whether the amount of virus in wastewater is minimal, low, moderate, high or very high. Viral activity in wastewater may indicate the risk of infection in an area,” the CDC said.

Wastewater data helps public health officials allocate resources and make informed decisions about mask and vaccination policies.

According to the CDC, viral activity in wastewater is currently required by law for COVID-19.