WASHINGTON – A United States government research team found no significant physical evidence of brain injury in a group of federal employees suffering symptoms of the Havana syndrome ailment that emerged in 2016, according to studies published in a medical journal on March 18.

National Institutes of Health (NIH) researchers also found no differences in most clinical measures between a group of 86 employees and their adult family members reporting unusual health incidents and a group of healthy volunteers with similar work assignments.

Symptoms of the mysterious ailment, first reported by US embassy officials in Cuban capital Havana and later afflicting diplomats, spies and other personnel worldwide, have included one hearing noises and experiencing head pressure, followed by headache, migraines, dizziness and memory lapses.

“These individuals have symptoms that are real, distressing and very difficult to treat,” Dr Leighton Chan, NIH Clinical Centre acting chief scientific officer and lead study author, said on a call to discuss the findings published in medical journal Jama.

Study participants, including personnel who had been stationed in Cuba, China, Vienna and the US, underwent a battery of clinical, auditory, balance, visual, neuropsychological and blood testing.

They also received different types of MRI scans aimed at investigating volume, structure and function of the brain.

Mr Mark Zaid, a Washington-based lawyer who has represented Havana sufferers, said the findings of no significant medical differences between the two populations after time had passed “do nothing to undermine the theory that a foreign adversary is harming US personnel and their families with a form of directed energy”.

NIH did not immediately respond to a request for comment.

But Dr Chan said the studies could not rule out that an outside event caused the debilitating symptoms.

The new findings from two studies conducted from 2018 to 2022 do not match results from a study done at the University of Pennsylvania in 2019, which showed subtle brain changes in those affected.

Dr Chan said the NIH used more rigorous MRI imaging protocols and a control group more closely matched in terms of work activities and location.

The researchers in a statement later said if the symptoms were caused by some external phenomenon, there is no persistent physical evidence, but acknowledged the possibility that such evidence is no longer detectable by methods they used.

An accompanying Jama editorial from Dr David Relman, a professor at the Stanford University School of Medicine, noted that earlier studies concluded that some of the cases could be plausibly explained by exposure to radiofrequency energy.

NIH researchers did find that more than a quarter of patients reporting symptoms developed a chronic condition called persistent postural-perceptual dizziness.

They also reported significantly increased symptoms of fatigue, post-traumatic stress and depression, compared with the control group.

The MRI brain imaging results “should be some reassurance for patients”, since researchers did not find a link between unusual symptoms and neurodegenerative changes, said study investigator Louis French, from Walter Reed National Military Medical Centre.

“The post-traumatic stress and mood symptoms reported are not surprising given the ongoing concerns of many of the participants,” he added.

The US State Department on March 18 said it was reviewing the NIH report on what the department calls anomalous health incidents (AHI).

A spokesman said Secretary of State Antony Blinken was determined the department would do “everything possible to ensure employees and family members who report an AHI are treated with respect and compassion and receive timely access to medical care and all benefits to which they are entitled”.

US intelligence agencies in 2023 concluded that it was “very unlikely” a foreign adversary was responsible for the Havana syndrome cases.

The agencies suggested in that report that symptoms reported by US personnel were likely the result of pre-existing conditions, conventional illnesses and environmental factors. REUTERS