On August 24 we ran a short brief saying Stanislaus County had confirmed its first human West Nile case of the year. That was accurate and it is now out of date. As of the state's September 4 update the county is at five human cases, and California is at 86.
5, per the state's September 4, 2026 update.
120.
86, across 21 counties.
6.
What changed since our first brief.
Our August brief covered one confirmed case. The number that matters more than the case count is the mosquito surveillance behind it, and that has been climbing all season. Positive mosquito pools in this county went from 25 in the week ending August 14 to 28 the following week, and the state now lists 120 positive mosquito samples in Stanislaus for the year.
Statewide the season is running hot by every leading indicator. Dead bird positivity through mid-August was about 24%, against a five-year average near 13%. Mosquito positivity was roughly 8 per 1,000 tested, against a five-year average of 5. Those two numbers move before human cases do, which is why public health officials were describing 2026 as a severe season while the human count was still small.
For scale.
California had 46 human cases by August 21 this year. At the same point in 2025 the figure was 14. Of those 46, about 87% were the neuroinvasive form, which is the serious presentation that affects the brain and spinal cord rather than the milder fever illness. By September 4 the statewide count had reached 86.
Human cases in California typically peak from August into September. That means the current count is not the season's final number, and the next few weeks are the part of the year that matters most.
The four things worth actually doing.
County health guidance is the standard four. Use a repellent containing DEET. Take extra care at dawn and dusk, when the mosquitoes that carry this are most active. Keep doors and window screens in working order. And drain standing water on your property — that is the one most people skip, and it is the one that stops mosquitoes from being produced in the first place.
Standing water in the 209 in September is not usually a pond. It is a saucer under a potted plant, a tarp with a dip in it, an unused wheelbarrow, a clogged gutter, a bucket by the hose bib. A week is long enough.
Why we are updating rather than rewriting.
The August brief stays where it is with its own date on it. This is a separate page with a separate date. We do not quietly edit an old article to make it look like we had newer information than we did. If the count changes again, there will be another one of these.
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