WADA have confirmed the department have nearly finished DNA analysis work and comparing blood bags with samples from suspected athletes.

WADA's director of I&I Günter Younger said last November that DNA had been extracted from 35 samples from frozen bags of blood and plasma.

The bags were seized from the clinic run by Spanish doctor Eufemiano Fuentes in Madrid back in 2006, following a police raid, and are being stored in a WADA-accredited laboratory outside of the country.

While cyclists have been largely linked with the scandal, athletes from other sports are allegedly also involved.

A "multi-phase plan" to identify the athletes possibly linked to Fuentes based upon available documents, reports from the police, the Madrid Laboratory, interviews with experts and research on media reports has been created by the I&I department.

Samples from suspected athletes were then sourced for comparison to the DNA extracts.

While the process is reaching a conclusion, the passing of the statute of limitations in 2014 will prevent athletes from being named or sanctioned.

A WADA spokesperson told insidethegames a decision will be taken by WADA management, based on legal advice, on the next steps after the I&I department complete their work.

The organisation said they will continue to pursue all possible legal options regarding the case.

This potentially could involve the names of the athletes being shared with International Federations and National Anti-Doping Organisations on a confidential basis.

WADA have expressed frustration at a "very limited and disappointing outcome" for athletes and the organisation.

"We will not be able to publish the names of those athletes because the eight-year statute of limitation passed on this case in 2014," a WADA spokesperson told insidethegames.

"This is due to the very significant time taken by the Spanish justice system to provide WADA and other anti-doping organisations involved with samples taken from the blood bags.

"While a number of athletes have been sanctioned some time ago in relation to Operation Puerto, it is fair to say that from WADA's perspective, we faced many obstacles and difficulties in this case, and invested significant resources over the past 12 years to get to the bottom of this case for a very limited and disappointing outcome.

"The Spanish legal system did not make our life easy and we never received any official support or assistance from any Spanish authority in this process.

"Several issues were identified in the way this file was managed by the Spanish courts and we have tried all that we could without success.

"This is extremely regrettable for clean sport and clean athletes."

Spain's Alejandro Valverde is among a small number of cyclists involved to have ever been outed, as well as Tour de France winner Jan Ullrich of Germany and Italy's Ivan Basso.

Top players from tennis, football and other high profile sports are also alleged to have been part of a doping ring, although this has never been proven.

Fuentes, who was found to have facilitated blood doping at his clinic, was given a one-year suspended sentence on public health grounds.

This was due to doping not being considered a criminal offence in Spain at the time.

Operation Puerto had impacted Spain's sporting image.

The initial case was considered to have harmed Madrid's bid for the 2020 Olympic and Paralympic Games, eventually won by Tokyo.