Short answer: because the seed travels, and the sprouts do not travel far at all. Recalled alfalfa sprouts from the current outbreak went to two states. Sick people turned up in fifteen. The seed lot is the part of the chain that crosses the map.
This pattern shows up in sprout outbreaks over and over, and it explains why investigators keep chasing seed instead of facilities.
What a seed lot is
A lot is one batch of seed that shares a history: grown in the same fields in the same season, cleaned in the same run, stored in the same conditions. It gets one identifying number, and that number is how the entire food safety system finds it later.
Alfalfa seed is a commodity crop. A single lot can run to tons, and a distributor splits it into bags for whoever orders. A sprout grower ordering 50 pounds at a time has no way of knowing which other companies bought from the same pile.
One pound of alfalfa seed yields roughly eight to ten pounds of sprouts, and a 5-oz package holds a third of a pound. A single bag becomes hundreds of packages. A lot becomes tens of thousands.
Why contamination hides inside a lot
Contamination in a seed lot is almost never uniform. It arrives in the field through irrigation water, wildlife or manure, and it lands in patches. Mixing and bagging spreads those patches unevenly across the whole lot.
That is why testing finished sprouts is a weak control. A negative result on one package says something about that package. It says very little about the next pallet, and nothing at all about the bags that went to a different company.
Sprouting then amplifies whatever made it through. Seeds sit warm, wet and dark for days, which is a decent description of an incubator. A few cells in a hot spot become a population large enough to make someone sick, and the finished crop is eaten raw.
The federal produce rule tries to close this with two controls aimed at the seed: treat it before sprouting, and test the spent irrigation water from every batch, because bacteria multiplying on the seeds show up in the water around them. Both are better than testing the finished product. Neither is absolute. Both controls land on the sprouter, and nobody is required to test the seed itself before it goes in: whose job it is to test sprout seed.
How the map ends up wrong
Here is the sequence that produces two recall states and fifteen case states.
- Illness first. Labs report infections, genetic sequencing links them into one cluster, and interviewers ask what people ate
- Product second. Receipts and restaurant records point to a brand, and that brand recalls what it can identify by lot and date
- Seed third. Traceback walks upstream from the grower to the distributor to the seed lot, which takes weeks and often ends at a company several steps removed from anything a shopper ever sees
- Everyone else last. Other buyers of the same lot are found by record review, and their products only get recalled once someone connects them
While that runs, the case map grows faster than the recall map. The recall covers one company’s confirmed distribution. The illnesses cover everything the seed touched, including the products of growers nobody has publicly connected yet.
In the current outbreak the FDA has already confirmed that at least one additional grower received the implicated alfalfa seed lot, and the seed supplier has not responded to the agency’s recall request.
Two more reasons the counts diverge
Distribution records are imperfect. A wholesale distributor in Minnesota sells to customers who resell across state lines, and the paperwork stops at the first buyer. The FDA says openly that recalled product may have reached states beyond the two it can confirm.
People move too. Someone eats a sandwich in Wisconsin, drives home to Florida and gets sick there, and the case is counted where they live.
What this means if you grow
The lesson from every sprout outbreak of the last thirty years is the same: the seed is the control point, and everything downstream is damage limitation.
- Buy seed sold for sprouting or microgreens, with a lot number on the package and a supplier who will tell you where it came from
- Record which lot went into which tray or jar, and keep the record after the crop is sold
- Hold a sealed sample of every lot. If a customer gets sick, that sample is the only way to clear yourself or find the problem
- Change one thing at a time when you switch suppliers, so an unfamiliar result has one plausible cause
Growing microgreens in a tray puts you in a better position than jar sprouting, because the seed hulls and the root mat leave with the tray and the crop is cut above them. The seed is still the input you cannot inspect by eye, which is why the paperwork matters more than the rinse.
Bottom line
One contaminated seed lot can produce illnesses in more states than any single recall will ever cover, because the lot is shared and the finished product is not. When the case map is much wider than the recall map, the investigation is usually still upstream of the company that sold the seed. The US traceability rule was written to close exactly this gap, but its enforcement has been pushed to July 2028.
What to do with that as a buyer, and why the seed lot matters more than the rinse, is covered in our food safety guide for microgreens, sprouts and leafy greens.
Sources: FDA outbreak investigation page for sprouts, August 2026; CDC outbreak page updated September 1, 2026; FDA produce safety rule requirements for sprout operations.
