SEVILLE, Spain (AP) _ Spiked food supplements are apparently responsible for the recent flood of positive tests for the banned steroid Nandrolone, track and field's medical chief said Friday.

Arne Ljungqvist, chairman of the International Amateur Athletic Federation's medical committee, said athletes may have ingested Nandrolone unwittingly in unlabeled over-the-counter supplements.

``It may be totally inadvertent,'' he said in an interview on the eve of the World Championships, which have been overshadowed by a series of high-profile doping scandals.

Experts have been puzzled by the sudden resurgence of Nandrolone, a muscle-building drug that has been around for decades and detectable in urine tests for years.

Sprint stars Merlene Ottey and Linford Christie are among those athletes who have tested positive for Nandrolone. On Friday, Dutch sprinter Troy Douglas' name was added to the growing list.

The wave of Nandrolone cases spread Friday to the Arab Games in Amman, Jordan, where two Moroccan women athletes were stripped of their medals after positive tests.

``The seeming epidemic spread of this stems from food supplements spiked with Nandrolone,'' Ljungqvist said. ``The problem is that athletes may have taken it without real control. The food supplements may not have been labeled.''

Supplements, increasingly popular with athletes looking for a legal way to sharpen their fitness and performance, are readily available.

``The producers of food supplements are not producing solely for the sports community,'' Ljungqvist said. ``They do it for the general public, for elderly people. In some countries, even today, some of the banned substances are not looked upon as pharmaceutical drugs.''

Ljungqvist said the unusually high number of veteran athletes being caught could be the result of their reliance on food supplements to stretch their careers an extra few years.

Ottey and Christie are 39, Douglas is 37.

Under IAAF rules, an athlete is considered guilty of a doping offense based on the presence of a banned substance in his body _ regardless of how it got there.

Ljungqvist said this policy will not change even if athletes took Nandrolone unwittingly. But he said athletes could have a legal case to challenge any suspension from the sport.

``If the athlete can clearly show that he has got a contaminated substance or food supplement from somewhere, then it's up to the lawyers to evaluate,'' he said.

Ljungqvist cited a recent case in his native Sweden of an athlete who took ``what was supposed to be a pure substance and turned out to be contaminated. He was disqualified from competition but exonerated from any further ban.''

Ljungqvist said the burden of proof would be on the athlete.

``The athlete has to make sure that no banned substance enters his body,'' he said. ``He is responsible. The athlete can't just claim, `I didn't know.' He has to give solid proof.''