Caldean Acute Cardiopulmonary Syndrome, or CACS for short, is a disease affecting the cardiopulmonary system of the person infected. Advanced scans or transporter's biofilters can pick up infected persons not showing signs or symptoms of the disease (the early stages).

In later stages, CACS causes the circulatory and respiratory systems to gradually fail, leading a cascading systems failure, leading to cardiac arrest and death. A cruel disease, CACS also has been known to cause cardiac arrest only to revive the ill person for more suffering.

CACS is a disease native to Caldea IV. On an earlier Starfleet expedition to the colony there, an officer was infected and spread the disease to most colonists, decimating the colony's population. With the biofilters active on the ship, transporters deflected the officer's signal to a derelict supply station in orbit, where, approximately 12 weeks later, he died.

In 2372, Captain Noah Wrightson was infected with a variant of CACS, and, like his predecessor, his transporter signal was transferred to the supply station. USS Cantabrian Drs. Marie and Helena Bourget successfully found a treatment to counter the variant, leading to Wrightson's successful recovery. (Star Trek: The Cantabrian Expeditions: "Isolation")

We assume that CACS was so contagious that neither a quarantine field or the combination of a quarantine field and styrolite would work to contain CACS. With the isolation bays aboard the Cantabrian rendered inoperative, transporters automatically beamed Wrightson to the next most isolated area: the supply station in Caldea IV's orbit.
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