According to a CBAt statement, sprinters Bruno Lins Tenorio, Jorge Celio Sena, Josiane Tito and Luciana Franca, and heptathlete Lucimara Silvestre had tested positive for the banned substance Recombinant EPO.
The CBAt said the five had asked for the B sample to be tested and would return home.
"The athletes -- who are banned from taking part in competitions until the results of the respective counter-tests are known -- are returning home, accompanied by their coaches... and prefer to present their defence in (their own) country," the statement said. "Due to the seriousness of the incident, the CBAt has ordered an administrative inquiry."
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