It started with a phone call that Dr. Michael Hoffer said he had never received before in his career – not even after serving 21 years in the military.
The call came last year in February. Hoffer answered, and he heard: “This is the State Department. We have a problem.”
Hoffer was told that an individual in Havana was hearing odd noises, experiencing pain and ringing in the ear, and feeling dizzy and confused.
That person, and others with similar symptoms, were United States diplomatic personnel living in Cuba – and the cause of their symptoms remains a medical mystery.
In August 2017, State Department officials said the cause may have been a possible “acoustic attack” using sonic devices. Cuba officials have arduously denied such an attack.
Hoffer, a professor of otolaryngology and neurological surgery at the University of Miami Miller School of Medicine in Florida, examined some of those personnel along with his colleagues.
Now Hoffer and his colleagues – from the University of Miami and the University of Pittsburgh – are revealing new details on those symptoms seen among the 25 diplomats in a study, published in the journal Laryngoscope Investigative Otolaryngology on Wednesday.
In this retrospective study, the researchers described their findings as “the first report of the acute symptoms in this patient group.”
A separate study, previously published in the medical journal JAMA in March, described the symptoms of 21 personnel who sought medical attention and found that a majority of them reported problems with memory, concentration, balance, eyesight, hearing, sleeping or headaches that lasted more than three months. Three people eventually needed hearing aids for moderate to severe hearing loss, and others had ringing or pressure in their ears according to that report.
Beginning in 2016 and throughout last year, several diplomats and their family members stationed in Havana reported hearing bizarre noises and experiencing a range of symptoms, such as dizziness, ear pain, and ringing in the ears.
When it comes to exactly what they were suffering from, “what caused it, who did it, why it was done, we don’t know any of those things,” Hoffer said during a news conference on Wednesday.
The US State Department and federal investigators have been unable to definitively attribute the source or cause of these symptoms, but in August last year, several department officials told CNN they might have been the result of an “acoustic attack” using sonic devices.
Cuban officials have strenuously denied that there were any targeted attacks on diplomats in Havana and said their symptoms could have been caused by other factors.
“All has been speculation or manipulated information,” Cuba’s Director General for US Affairs at the Cuban Foreign Ministry, Carlos Fernandez de Cossio, said on Wednesday about the US investigation into the health incidents.
“The concrete questions have not been asked. Why has the US government not been ready to cooperate with Cuba? What is the US government hiding? Why is it not capable of putting forward concrete, real information that the scientific community can accept?”
The study released Wednesday details symptoms experienced by 15 men and 10 women.
They all reported being exposed to either some strange noise or pressure and then immediately after that exposure, the majority felt intense ear pain and ringing, according to the study. They all then noticed cognitive symptoms, including feeling disoriented.
The study noted that some of the findings may seem similar to symptoms of a “mild traumatic brain injury following blast exposure or blunt trauma.”
“It does not seem imprudent to speculate that a highly specific unidentified energy exposure, perceived as a sound or pressure, could be producing an inner ear disturbance or demonstrate findings suggestive of an mTBI,” or mild traumatic brain injury, the researchers wrote in the study.
Yet the injury pattern seen among these patients had some differences from the typical symptoms seen with a concussion or mild traumatic brain injury, the researchers noted.
“In addition, the low incidence of headaches (around 25%) is unusual, as many studies of mTBI show that headache is one of the most common and persistent symptoms,” the researchers wrote.
Since the exposure responsible for the study’s findings remains unknown, the researchers wrote, they could not “exclude any potential directed or non‐directed energy sources at this time.”
Directed energy sources would be some form of energy pointed or focused directly on an object or a person, Carey Balaban, a professor in the Department of Otolaryngology at the University of Pittsburgh and one of the authors of the study, said in the news conference on Wednesday.
“The energy may be acoustic, pressure waves, you’ve probably heard of LRAD devices (or long-range acoustic devices) – devices they’ve discussed in the press – so ultrasound is one mode that could be used for this. We also could have radiofrequency. We could have microwave. We could have light – lasers are an example of it. I’m going through these just as examples,” Balaban said.
“I want to make it eminently clear that we don’t know what they were exposed to and certainly can’t make any inferences as to whether it was deliberate or inadvertent,” he said.
Authorities have used long-range acoustic devices, or LRADs, to disperse crowds of protesters with a loud, painful sound over a long distance. Some countries have used a “mosquito” – which produces a very high-pitched sound that can be perceived by teenagers but not adults – to prevent teens from loitering.
“I know of no acoustic effect that would produce concussion-like symptoms; according to my research, strong effects on humans require loudness levels that would be perceived as very loud noise while exposed,” Jürgen Altmann, a physics professor at Technischen Universität Dortmund in Berlin, told CNN in May.
Limitations of the new study include that a small number of patients with symptoms were evaluated and uncertainty remains around the true cause of the symptoms.
Get CNN Health's weekly newsletter
Sign up here to get The Results Are In with Dr. Sanjay Gupta every Tuesday from the CNN Health team.
“The way we view this is that it’s an area for active research,” Balaban said.
“I’m currently doing some research sponsored by the Office of Naval Research, where we’re looking at using computer simulation and a variety of physical and biological models to just get an idea of what are likely possibilities,” he said. “We’re not ready to rule anything out yet but we’re ready to find evidence so that we can rule things out. We have no favored cause.”
CNN’s Patrick Oppmann and Michael Nedelman contributed to this report.