The Centers for Disease Control and Prevention will lead an investigation into the cross-border sewage crisis, measuring the potential health impacts on people who live and work near where millions of gallons of sewage spill over the U.S.-Mexico border from Tijuana, county officials said Thursday.

In cooperation with the county, state and San Diego State University, the investigation by the federal public health agency will involve door-to-door interviews with several hundred households in South County to assess how exposure to polluted water and air in the region is affecting people’s health. It will also look at occupational and other environmental exposures and concerns in at-risk populations.

The process is formally known as a Community Assessment for Public Health Emergency Response, or CASPER. These assessments are usually quick and produce data about what a community needs “so public health leaders and emergency managers can make informed decisions,” according to the CDC’s website.

It is not known how the CDC, which did not immediately respond to a request for comment, will select households and when it plans to launch the effort.

The effort marks the most comprehensive look to date by government agencies at the health impacts persistent sewage spills and odors are having on people in the county’s southwest region.

It also comes in response to repeated calls from the public and local elected officials to investigate pollution-related health concerns. While both countries work on repairing treatment plants, concerns have grown in recent years about the short- and long-term effects of living and working near the pollution. In addition to beach closures and economic downturns, people have reported symptoms such as chronic coughs, headaches, nausea, vomiting and diarrhea.

“Raw sewage flows, and the associated odors and potential for disease, should not be anyone’s everyday worry,” Ankita Kadakia, interim County Public Health Officer, said in a statement.

Officials said the CDC and county are finalizing an agreement for the community assessment, but have already verbally agreed to conduct an epidemiological investigation, otherwise known as an Epi-Aid.

An Epi-Aid is a study of “an urgent public health problem, such as infectious or noninfectious disease outbreaks, unexplained illnesses, or natural or manmade disasters,” according to the CDC’s website. Such investigations typically last one to three weeks and are generally conducted onsite.

After formally requesting an Epi-Aid this summer, the county and federal health agency have been working to determine the kind of immediate help it can offer to address afflicted communities.

A similar investigation took place in Flint, Mich., in 2016 to investigate a water crisis there. When the city changed its municipal water supply source from the Detroit-supplied Lake Huron water to the Flint River, pipes corroded and contaminated drinking water with lead. The CASPER found that many local households had experienced worsening mental health, including signs of depression and anxiety or stress.

“(CASPERs are) really a great way to kind of assess the public health needs of a community and a great way to get some representative data,” said Dr. Seema Shah, medical director of the county’s epidemiology and immunization services branch.

The effort also follows a two-week investigation by the county in February that showed no evidence of increased gastrointestinal illness at a South Bay health clinic that claimed its patients suffered such symptoms. Some San Diego researchers and elected officials had pushed back on the county’s findings, questioning whether the data collected was sufficient to conclude that people who do not come into direct contact with polluted water cannot get ill.

County officials acknowledged that symptoms aren’t always reported traditionally and that there are information gaps.

“That’s the big point about the CASPER,” said Kadakia. “This is going to give us the data that we have been looking for in order to capture things we may not be seeing in reportable illness. But be able to have a way to validate those concerns that the community has been expressing and be able to try to form action plans.”

The county also said it is expanding its public reporting on health issues in the South Bay. Earlier this year, it launched a “surveillance bulletin” that has been monitoring the prevalence of gastrointestinal symptoms observed among recent emergency department patients, such as diarrhea and vomiting. Starting this week and updated every Wednesday, the website will include respiratory illness surveillance, tracking asthma or chronic obstructive pulmonary disease symptoms, including reactive airway disease, wheezing, and bronchospasm.

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(Reporter Paul Sisson contributed to this report.)

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