Airport officials found a small can of self-defense pepper spray attached to a key chain on the floor near the second-floor security checkpoint in Concourse B, which serves international flights, said Miami-Dade Fire Department spokesman Jeff Hackman.
"This could be the source of the sickness," Hackman said.
Paramedics treated and released 43 people who were in or near the checkpoint for trouble breathing and other symptoms, including scratchy throat, watery eyes, coughing and sneezing, Hackman said. Fire officials could not say how many people total were forced out of the concourse, one of eight at the airport.
The symptoms are consistent with those caused by pepper spray, Hackman said.
An airport employee began coughing and vomiting when she came upon the canister. A hazardous materials team was testing the small black can to determine what was inside.
"I saw my co-workers were crying, they couldn't breathe, they were scratching themselves," said Mayelin Rodriguez, a screener with Global Aviation Services in Concourse B.
Several fire units and ambulances converged outside the section of the airport leading to the concourse shortly after someone called in the report around 10 a.m.
At least five American Airlines flights scheduled to depart from Concourse B were reassigned to other gates because of the delay caused by the incident, said Alicia Diaz, an airport spokeswoman.