>> Hi, Mr. Lang.
It's Dr. Hayes, the epidemiologist
from the state health department.
>> Hi, Dr. Hayes.
>> I hope you're feeling better since our last phone call
about your Salmonella infection.
I'm calling because others are sick with the same bacteria
and we're worried that this might be an outbreak.
Can I ask you some more questions
about what you ate recently?
>> Sure. I'm happy to answer your questions.
I'd hate for anyone else to get sick.
How do you know we have the same bacteria?
>> Well, the lab determined that the DNA fingerprint
of the bacteria that made you sick was very similar
to the fingerprints of bacteria
that have made other people sick around the country.
One of our lab scientists, Dr. Gray, is here with me.
She can explain how the lab identified the bacteria.
>> Nice to speak with you, Mr. Lang.
Are you feeling better?
>> A lot better, thanks.
I never want to get that sick again.
How did you figure out I have the same Salmonella that's
making others sick?
Dr. Hayes mentioned some kind of DNA fingerprint.
>> Yes, DNA, more specifically, the DNA sequence, is what we use
to determine if people are sick with the same kind of bacteria.
It's a complicated process that uses a stool sample.
Here's how it works.
When we received your stool sample, we streaked it
on a culture plate that allows all the bacteria in your stool
to grow, including the bacteria that made you sick.
The colonies from each bacteria can look different on a plate
and we can recognize them based
on their appearance along with other lab tests.
In your sample, we identified Salmonella.
All bacteria contain genomes made up of DNA.
The DNA sequence tells the bacteria how
to eat, grow, and multiply.
It's unique to each bacteria and can be referred
to as a "DNA fingerprint."
For outbreak investigations, we compare the DNA fingerprint
of the bacteria that made someone sick to the fingerprint
from another sick patient.
If the two DNA fingerprints are identical
or very similar, then we have a match.
>> So how do you read a bacteria's genome
to know what its DNA fingerprint looks like?
>> Good question.
The process is called "whole genome sequencing."
Every bacterial cell has a genome that has DNA.
We take millions of genomes and cut them
into pieces small enough to fit into a DNA sequencing machine.
>> Millions?
>> Yes. Then we mix them together
and feed the pieces into the machine.
The information is sent to a computer and reassembled
into a single copy of the genome,
so we can compare one bacterial genome to others.
>> That sounds like a really complicated puzzle.
>> Yes, it is.
That's why we have really powerful computers.
We then compare the DNA fingerprint of the bacteria
that made you sick to those of the bacteria
that made others sick.
>> And that's where we come back in.
Once the lab tells us that several
of the same bacterial DNA fingerprints have been
identified, we begin investigating to figure
out if we have an outbreak and, if so, what's causing it.
We ask people, like you, about the foods they ate
and the things they did in the weeks before they got sick
to try and find a common food among everyone.
>> Wow, that's great.
>> Yes, it is.
We have a network called PulseNet that allows us
to connect foodborne illnesses all
over the country to detect outbreaks.
This network has prevented 270,000 people from getting sick
and saved the U.S. over half a billion dollars every year.
Whole genome sequencing has made PulseNet even better.
>> That's amazing.
>> PulseNet works because of people like you.
You helped us by going to your doctor when you got sick
and answering our questions about where you were,
what you were doing, and what you ate before you got sick.
Working together,
we can identify contaminated food quickly before more people
get sick.
That's ultimately our goal.
>> Thanks for explaining whole genome sequencing.
Dr. Hayes, I'm ready to answer your questions.