Locally acquired Chagas disease is exceedingly rare in the United States:
28 documented cases between 1955 and 2015.
In October 2017 a woman aged 53 went to donate blood in Missouri. On **25
October** she was told her donation had screened positive for antibodies to
Trypanosoma cruzi, the parasite that causes Chagas disease. A
confirmatory enzyme strip immunoassay on 8 November was also positive, and
CDC's own testing of her serum was consistent with infection.
Physicians found no clinical symptoms. She had no travel history
suggesting risk, no occupational exposure, and had **never received a blood
transfusion or organ transplant.**
By elimination, the exposure happened in Missouri.
Why that is notable and not surprising
**The insect vector — triatomines, "kissing bugs" — has been identified in
Missouri before.** What had never been identified was a human case acquired
there.
So the vector was known to be present and the disease was assumed not to be
transmitting. This case is the first evidence that it does, in a state nobody
was watching for it.
How it was found matters as much as what was found
She had no symptoms, and Chagas disease is dangerous precisely because of
that: the acute phase is mild or silent, and decades later it can cause heart
and digestive disease in a minority of those infected. Nothing would have taken
her to a doctor.
She was found because blood donations are screened. A programme designed to
protect recipients turned up a case of local transmission that no clinical
system would ever have seen — and, in doing so, told a state something about
its own epidemiology.
That is also the limit of the finding. **Blood donor screening only sees blood
donors**, so a single case discovered this way says nothing about how many
others there are.
What it asks of clinicians
**Although most documented cases are among persons originally from Latin
America, health care providers and public health professionals should be
aware of the possibility of locally acquired Chagas disease in the southern
United States.**
The association between Chagas disease and Latin American origin is
statistically sound and diagnostically dangerous: a patient with no travel
history is the one who will not be tested.
Source: Centers for Disease Control and Prevention, MMWR.
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