"We've learned that, under extreme stress, there can be massive, life-threatening complications," said Dr. Jon Thogmartin, the Pinellas and Pasco County chief medical examiner.
Long before sickle cell trait was linked to deaths, it was lauded as a miraculous gene mutation that protected the body againstmalaria.
Africa and the Mediterranean region of Europe have the world's highest rates of malaria exposure.
According to the National Institute of Health, 8 percent of African-Americans in the United States have the trait. Less than one percent of the non-African-American population here carries the trait, including Georgia head football coach Mark Richt's son, David.
The numbers are much higher some places outside of the U.S. A study published in 2004 found about 30 percent of people living near the Congo in Africa had sickle cell trait. Other studies since then have found that about 10 percent of people in Jamaica and 15 percent of people in Haiti have the trait.
As a result, a larger percentage of children of recent immigrants from those regions likely have the trait. The three Florida athletes who died — Florida State's Devaughn Darling, UCF's Plancher and Wekiva High's Louis — were all children of Caribbean immigrants.
After Lloyd's death following the Rice workout, his parents sued the NCAA for failing to require all schools to test for the trait. As a result of a settlement with the family, the NCAA began a screening program last year. All Division I athletes are now either tested for sickle cell trait or must sign a waiver indicating they do not want to be tested.
The NCAA has not released a breakdown of how many athletes tested positive for the trait. However, The Institute for Diversity and Ethics in Sport released a study indicating 11,924 athletes played at the Football Bowl Subdivision level in 2010. Based on the figures, it is likely about 670 players competing at the highest level of college football last season had sickle cell trait.
Sickle cell trait is at the heart of a controversy within the medical community, with one side arguing it sometimes causes sudden death and others arguing it could not possibly cause someone to die.
Critics suggest deaths are incorrectly being tied to sickle cell trait, ignoring issues such as heat stroke and heart problems that are the true causes of death. They suggest any changes to red blood cells occur naturally after a person with sickle cell trait dies because the body is deprived of oxygen.
Thogmartin, the Pasco and Pinellas chief medical examiner, adamantly disagrees.
He recently co-wrote a Journal of Forensic Sciences article documenting 16 people who died from sickle cell trait complications since 1996. He argues pathologists review a long list of factors besides warped red blood cells to determine whether a death could be caused by sickle cell trait complications.
Some critics of the NCAA's sickle cell trait testing policy argue schools may discriminate against athletes who have tested positive for the trait.
In 2007, the National Athletic Trainers' Association said sickle cell trait should not disqualify athletes from participating in sports. Researchers have documented cases of high school, college, pro and Olympic athletes with sickle cell trait who completed their careers with zero health problems cause by the condition. NFL stars Terrell Owens and Santonio Holmes are among a long list of NFL players who tested positive for sickle cell trait but have not suffered any trait-related health problems.
"There's never been any statement or study that I'm aware of that has said that sickle cell trait is a contraindication," said Oklahoma head athletic trainer Scott Anderson, co-chairman of the group that developed the National Athletic Trainers' Association consensus statement on sickle cell trait. "If everyone follows precautions, there is no reason athletes can't perform at the highest levels."
A committee of about 40 people, including 15 doctors and 13 certified athletic trainers, met to develop the NATA's guidelines for treating athletes with sickle cell trait.