Cyclospora keeps climbing, a bad West Nile season, truck spraying, and good news
The Dose (July 14)
The YLE team is back from summer break, tanned (some of us), rested (debatable with small kids), and ready to jump right back in.
I know a lot of you have questions about the Cyclospora outbreak. The YLE team is collecting them all, and tomorrow I’ll pick the top 10 for a deep dive. As of this morning, there is still very, very little communication from HHS, which is pretty insane.
In the meantime, here’s what’s going on with health this week, including other bugs like ticks and mosquitoes. Expect trucks to be spraying insecticide soon, and let’s celebrate an enormous public response to a new proposed federal rule.
Disease weather report
Cyclospora keeps climbing
Cyclospora cases continue to climb. Some of this is expected, since more people are now aware of it and testing for it, but it is still an undercount, given that many people wait out the sickness at home.
The total number of cases is hard to pin down. This is because data in the U.S. is decentralized (local health departments report to states, states report to the CDC), so you will likely see numbers all over the place. If we scrape for state-level data, the most cases (2,640) are in Michigan, followed by New York (470). A local health department in Northwest Ohio is reporting 661 cases.
While there are cases in over 30 states, the U.S. sees cases every year, often from different outbreaks. A key question is whether the number exceeds expectations and, if so, why. In some states, this is certainly the case. For example, the number of infections in Michigan is 31 times higher than in previous years, and in New York, it’s three times higher. In some states, like California, rates are not higher than normal.
Michigan’s health official announced yesterday that preliminary findings indicate lettuce or packaged salad greens as a likely source. The investigation has yet to pinpoint a company or rule out other foods. Two dozen other states are still under active investigation. Zero word from FDA.
What this means for you: Continue to avoid bagged and boxed salads at grocery stores and restaurants. I’m still sticking to produce that can be peeled or vegetables with smooth surfaces, like cucumbers, until more data comes in.
Ticks are backing off
We’re well on our way down for tick season. Activity tends to drop off as we move deeper into the heat of summer.
Why? Ticks are prone to drying out, so in peak summer heat they retreat into moist, shaded leaf litter rather than questing (climbing grass to grab a host), which reduces host-seeking activity even if the tick population hasn’t shrunk. This dip also lines up with the tick life cycle: nymphs, responsible for most Lyme transmission, peak in late spring/early summer, then quiet down in the hottest weather before adults pick back up in fall.
Mosquitoes taking over
As ticks recede, mosquitoes take over and with them, the rare diseases they can carry. The most common one in the U.S. is West Nile.
Peak mosquito season is still about a month out, but the CDC is already flagging an unusually early surge in West Nile virus (WNV) activity this year. They have flagged 48 cases across 23 states detecting the virus, which is more than five times the historical average for this point in the season.
What this means for you: Most people infected with WNV never even know it because ~80% have no symptoms. But older adults and those who are immunocompromised can develop serious neurological illness. Start being consistent with using an EPA-registered repellent (with DEET or picaridin), dumping standing water around your home, and using screens at dusk and dawn. You may also start seeing mosquito spraying trucks. (See more below.)
Heat blanketing the North
This week, a large swath of the northern U.S. is facing the most extreme heat risk category. If you’re in the purple or red areas, everyone is at risk and needs to take action. Heat kills more people in the U.S. than any other weather event.
What this means for you: Check on elderly neighbors and relatives, hydrate before you’re thirsty, and move strenuous outdoor activity to early morning or evening if you can. Here are 6 things to know about heat-related illness from the YLE team.
World Cup Health Security Center Update
We’re nearing the end of the World Cup tournament (the final is on July 19!), and there have been no major outbreaks tied to the games, aside from heat-related illness. A few teams reported minor illnesses among players.
Measles remains the primary focus of monitoring. There are a number of cases passing through major airports (far more than in any other year), particularly near the World Cup games. While it will be very hard to track, we could very well see outbreaks across the world following the World Cup.
Spotlight: Why is that truck spraying my street?
With mosquito activity picking up and the U.S. having a particularly bad start to the season, you may start noticing spraying trucks in your neighborhood. Where they go is driven entirely by your local public health or vector control department’s surveillance data. Departments set traps to collect mosquitoes, send batches to a lab, and test them.
When lab tests consistently yield positive results, insecticide is then sprayed in the affected area. The spraying itself does two things:
Kill flying adult mosquitoes by spraying very small amounts of adulticides into the air. This spray is a fine mist that acts as a fogger.
Kill larvae by applying larvicides directly to the water where mosquito larvae have been detected. This helps kill more hard-to-reach areas.
People rightfully have many questions about whether these insecticides are safe for humans. They are safe because the dose and where they are applied are very purposeful. These insecticides work by overstimulating insect nerve cells until they’re paralyzed, but insect nerves are far more sensitive to the chemical than ours, and mosquitoes are tiny, cold-blooded, and can’t break the chemical down the way we can. So the same dose that’s fatal to them is far too small to hurt a person. How these insecticides are used also matters. Adulticide sprays are released as low-volume mist, and the droplets disperse and degrade quickly, resulting in very low human exposure. Larvicides are placed directly in standing water and target larvae through mosquito-specific biological mechanisms.
A 2025 review of community mosquito-control spraying found no causal relationship between adult mosquito-control applications and adverse human health impacts when applied appropriately, with estimated exposure levels far below regulatory concern.
People with asthma and other respiratory conditions are particularly concerned. But an older study in New York City found no increase in asthma visits, including among children, after West Nile spraying.
What this means for you: Reducing WNV is important, and spraying is safe. I’ll stay indoors during spraying when I can but won’t lose sleep over it. Check with your local public health or mosquito control department for the schedule—they’re supposed to publish one.
Good news
More than 341,000 comments were submitted on the OMB’s proposed rule that could, quite literally, break science in the U.S. This is an enormous public response by any standard; public comment on federal rules almost never gets anywhere close to that volume. Way to show up for science discovery in the U.S.! Comments are now closed, and it’s time to see how the federal government responds.
Bottom line
From salad choices to mosquito bites to heat safety, this world just never gets boring. Stay healthy out there.
Love, YLE
Your Local Epidemiologist (YLE) comprises a team of experts, ranging from physicians to immunologists to epidemiologists to nutritionists, working together with one goal: to “translate” ever-evolving public health science so that people are well-equipped to make evidence-based decisions. The YLE suite of newsletters reaches over 475,000 people across more than 132 countries. This newsletter is free to everyone, thanks to the generous support of fellow YLE community members. To support the effort, subscribe or upgrade below:
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I appreciate you SO much. THIS is one of the outcomes of "increasing government efficiency and reducing waste". Great job, government........we will pay the price for decades.
On another note, I am concerned about the 'mass casualty' effect of mosquito spraying on all other insect species. Spraying is a very important public health intervention, but I do understand it to have long-lasting, far-reaching effects on other insects and creatures that we do not measure.
Thank you for all your efforts to keep us informed. It’s much appreciated.🤗