They found the outbreak by swabbing the bedding in the chick box

Salmonella causes an estimated **1.2 million US illnesses, 23,000
hospitalisations and 450 deaths a year**, and **about 11% come from animal
contact.** Backyard poultry is a growing share of that, and backyard poultry
mostly comes from **agricultural feed stores supplied by mail-order
hatcheries.**

Why tracing it back does not work

**When a hatchery doesn't have enough poultry to fill an order, it will often
enlist a second hatchery as a source**, and drop-ship — **ship under the
original hatchery's name and address** — directly to the customer.

So the name on the box is not necessarily the place the birds came from. **Real-
time environmental sampling at mail-order hatcheries rarely happens during
outbreak investigations because of the difficulty of tracing poultry to its
source.**

The method

Michigan stopped trying to work backwards and sampled at the point of arrival.
**As boxes reached feed stores, health department staff put the bedding and
liners into sterile collection bags** with gloved hands, and **photographed the
postal service labels.**

The photograph is the clever part:

**Although the address of the hatchery to which the order was placed appears
on the shipping label, postal service labels indicate the origin of the
shipment.**

The commercial label says who sold the birds. The postal label says where the
parcel was posted. One of those is the truth, and it was already on the box.

What it found

2016–2018: 136 samples, three feed store chains, 20 Michigan locations,
mostly in spring. The boxes came from **nine hatcheries, about 65% from a
single one in Michigan.**

A quarter of the boxes carried salmonella, and four of the six serotypes
matched outbreaks that were making people ill during the same period.

Results were shared with local health officials and the sampled feed store.

The whole method costs a bag, a pair of gloves and a photograph, at a place the
birds have to pass through anyway — which is why it works where sampling the
hatchery does not.

Source: Centers for Disease Control and Prevention, MMWR.