The apparent escape from a high-security lab of a dangerous bacterium that led federal officials last month to suspend research on certain high-risk pathogens at Tulane University has left questions about an ongoing investigation of the incident and broader risks.

According to a lengthy 1 March news article in USA Today, two rhesus macaques at the Tulane National Primate Research Center in Covington, Louisiana, that fell ill in early November later tested positive for infection with Burkholderia pseudomallei, which is found naturally in soil and water in Southeast Asia and northern Australia. Center researchers had been working with rodents on a vaccine for the bacterium, which can cause a sometimes serious illness called melioidosis in animals and people. The two macaques, which later had to be euthanized, and two other rhesus macaques that tested positive for the bacterium may have been exposed while being treated at the center’s hospital.

Adding to concerns, a U.S. Department of Agriculture (USDA) investigator who visited the site in late January fell seriously ill a day later and tested positive for Burkholderia pseudomallei. It is not clear whether the investigator, who has since recovered, was infected at Tulane or earlier during travel abroad, the Centers for Disease Control and Prevention announced in February. The agency said it had suspended all studies at the center involving select agents, a list of dangerous viruses, bacteria, and toxins that are tightly regulated. That includes about 10 projects, USA Today reports.

The hospital where the rhesus macaques were treated is located some distance from the biosafety level 3 lab where the vaccine research took place. According to the article, federal officials are still investigating the release of the bacterium. It has not been found in soil or water samples from the site, but USA Today cites studies and documents suggesting that the sampling was not done properly.

Tulane University said in a statement today: “Our work with Select Agents was suspended in February as a result of the USDA investigator falling ill after visiting the Tulane National Primate Research Center (TNPRC). Initial blood tests indicate that this investigator, who has since recovered, was not exposed to Burkholderia pseudomallei at the TNRPC. At present there is no evidence of Burkholderia pseudomallei in any human or non-human primate at the TNPRC.”

The Tulane incident follows several accidents with risky pathogens last year at U.S. high-containment labs that have fueled concerns about dual-use research, or studies of agents that could potential be used as bioweapons. Last summer, the government called for a nationwide search for forgotten pathogen samples in federally funded labs and a review of safety and security procedures.

And in October, U.S. officials halted new federal funding for 18 projects that tweak the influenza, SARS, or MERS viruses to make them more pathogenic or likely to spread among mammals. Federal officials and outside experts are now reviewing the risks and benefits of such “gain-of-function” studies to decide whether they should be allowed to resume.