County and federal public-health teams will return to South Bay neighborhoods next week for a second household survey on the health and daily-life effects of Tijuana River sewage pollution. The follow-up Community Assessment for Public Health Emergency Response, known as CASPER, is scheduled for Sept. 17 through 19.
The Centers for Disease Control and Prevention and San Diego County conducted the first assessment in October 2024. This round will use a new random sample of households rather than revisit the same participants. That design can estimate current community conditions, but it will not track changes within the same families over time.
Interviewers will visit selected homes from 2 to 7 p.m. Thursday and Friday and from 10 a.m. to 7 p.m. Saturday. The county says interviews take about 20 minutes, participation is voluntary and anonymous, and teams will wear badges and reflective vests. Bilingual English-Spanish staff will be included.
CASPER uses two-stage sampling. The survey area is divided into clusters, generally based on census blocks; 30 clusters are selected with larger areas more likely to be chosen. Teams then randomly select seven households within each cluster. County materials say the method is designed to represent 40,911 households across the South Bay and Tijuana River Valley region.
The 2024 survey contacted 480 homes, reached someone at 333 and completed 189 interviews, a 39.4% contact rate. Results were weighted according to each household's probability of selection. Weighting lets a limited sample describe a larger area, while the response rate and residents' willingness to answer remain important limits on interpretation.
The county says the need for another snapshot follows years of cross-border flows carrying untreated sewage, sediment and trash through the valley. Its study page points to more frequent infrastructure failures, year-round flows and two years of near-record rainfall as factors that elevated contamination. Those physical conditions affect recreation, sensitive habitat, public health and beach-water closures, but the household survey is designed to measure residents' reported experience of them.
That first assessment found 85.1% of households were somewhat or very aware of the sewage crisis. About 7.7% reported that someone in the home had contacted Tijuana River water in the previous month, and 16.2% reported contact with water at Imperial Beach, Tijuana Slough or Silver Strand during closures. Another 44.2% said they frequently avoided areas because of contamination.
The new questionnaire is intended to identify continuing concerns, changes since 2024 and support needs. It is a point-in-time measure of reported experiences, not a clinical study proving that a particular exposure caused an individual symptom. County officials say the comparison can still guide health education, communication, behavioral-health services, resource distribution and coordination with other agencies.
Results will be published on the county's CASPER page when available. That follow-through is central: a second survey is most useful when the sampling and weighting are explained, 2024 and 2026 questions are compared on like terms and officials connect findings to specific decisions. For residents asked to open their doors next week, the immediate contribution is 20 minutes. The public obligation is to show what changed because they answered.