West Nile Activity Is at a Five-Year High in California. Here’s What San Joaquin County Residents Should Do Now
West Nile virus activity has reached its highest level in California in five years, and San Joaquin County is already seeing signs of increased activity.
The county confirmed its first human West Nile infection of 2026 on August 5. Since then, statewide surveillance has continued to find the virus in people, mosquitoes and birds as California moves through the months when transmission typically peaks.
That does not mean Stockton and San Joaquin County residents should stop spending time outdoors or become afraid of every mosquito.
It does mean mosquito-bite prevention deserves more attention right now.
West Nile Activity Has Increased Since the County’s First Case
When San Joaquin County announced its first human case on August 5, it was the 12th human case reported in California that year.
California’s surveillance now reports 46 human cases in 14 counties and four West Nile-related deaths statewide. State health officials say West Nile activity is at a five-year high, and August and September are normally peak months for transmission in California.
The virus is also being detected locally.
As of the state’s latest county data, San Joaquin County has reported five West Nile-positive dead birds. State surveillance also reported 21 new positive mosquito samples from San Joaquin County in its latest weekly update.
A positive mosquito sample can contain multiple mosquitoes, so that number should not be read as 21 individual infected mosquitoes.
The practical message is straightforward: West Nile is circulating, and preventing mosquito bites matters.
Most People Who Get West Nile Never Become Sick
West Nile virus is most commonly spread to people through the bite of an infected mosquito.
According to San Joaquin County Public Health Services, about 80% of people who become infected develop no symptoms. About 1% develop serious illness.
People who do become sick can experience fever, headache, body aches, vomiting, diarrhea or a rash.
Severe illness can affect the brain and nervous system and may require hospitalization.
There is currently no licensed human vaccine to prevent West Nile and no specific antiviral treatment for West Nile virus. Medical care is supportive, meaning healthcare professionals treat symptoms and complications while the body fights the infection.
That makes preventing mosquito bites especially important.
Some People Face Greater Risk of Serious Illness
Everyone should take reasonable precautions, but the risk of severe illness is not the same for everyone.
San Joaquin County identifies people over 60, people with weakened immune systems, and people with diabetes or kidney disease as especially vulnerable. The Centers for Disease Control and Prevention also says the risk of severe illness increases with age and can be higher with certain chronic medical conditions.
If an older adult or medically vulnerable person lives in your household, mosquito protection should become part of ordinary daily planning during this period of increased West Nile activity.
Start With the Standing Water Around Your Home
One of the most useful things you can do takes only a few minutes.
Walk around your property and look for standing water.
Mosquitoes lay eggs in water, and the San Joaquin County Mosquito and Vector Control District recommends dumping and draining standing water every week.
Check flowerpots, buckets, children’s toys, rain barrels, clogged gutters, unused fountains, tires and other outdoor containers. Even small amounts of water can support mosquito development.
Residents with neglected swimming pools, significant mosquito problems or other mosquito concerns can contact the San Joaquin County Mosquito and Vector Control District and request an inspection.
The district also provides mosquitofish for ponds and certain permanent water features.
Take Extra Precautions at Dawn and Dusk
You do not necessarily need to stay indoors when mosquitoes are active.
You do need to protect yourself.
San Joaquin County advises residents to take particular precautions at dawn and dusk, when mosquitoes that can carry West Nile are most active. The county specifically advises extra caution during the first two hours after sunset.
When practical, wear loose-fitting long pants and long-sleeved shirts.
Use an insect repellent registered with the Environmental Protection Agency and follow the directions on the product label.
Recommended active ingredients include DEET, picaridin, IR3535 and oil of lemon eucalyptus.
Check Your Window and Door Screens
Mosquito protection should continue when you go inside.
Check window and door screens for holes, tears or poorly fitting edges that could allow mosquitoes into your home.
The local mosquito-control district recommends installing or repairing screens as part of protecting a home from mosquitoes.
This can be especially important when an older adult or medically vulnerable person lives in the household.
Know When Symptoms Need Medical Attention
Most mosquito bites do not lead to West Nile illness.
But it is important to know when symptoms deserve medical attention.
San Joaquin County advises people who know they have been bitten by mosquitoes and develop flu-like symptoms to consult a healthcare provider, especially if they have a weakened immune system.
If you develop severe symptoms such as a severe headache, high fever, stiff neck, muscle weakness, confusion, disorientation or tremors, seek medical care right away.
Severe West Nile illness can affect the brain and nervous system and may require hospitalization.
Mosquito Control Is Already Underway in Stockton
The San Joaquin County Mosquito and Vector Control District has conducted mosquito-control operations in several parts of Stockton and elsewhere in the county during this mosquito season.
Those operations have included areas of north, northwest, southwest and south Stockton. The district says treatments are based on surveillance data, including increased mosquito populations and detection of West Nile virus.
Residents can help with that surveillance.
Report significant mosquito infestations or neglected green swimming pools to the San Joaquin County Mosquito and Vector Control District.
Dead birds can also be reported because they help public-health officials track West Nile activity.
The statewide dead-bird hotline is 1-877-WNV-BIRD (1-877-968-2473).
The Goal Is Not to Stay Inside. It Is to Reduce the Bites.
California’s five-year high changes the context surrounding San Joaquin County’s first human West Nile case.
It does not mean every mosquito is infected.
It does not mean ordinary outdoor life has become unsafe.
It means residents have stronger reason to make mosquito prevention part of everyday life during the remaining mosquito season.
Drain standing water.
Use repellent.
Take extra precautions around dawn and dusk.
Repair damaged screens.
Know whether someone in your household faces greater risk.
Know which symptoms should lead you to seek medical care.
These are small actions, but they are the actions Stockton and San Joaquin County residents can take right now to reduce their risk of West Nile virus.