A preliminary case report on the victims of mysterious “health attacks” in Havana, Cuba details the results of extensive clinical evaluations, concluding that the individuals appear to have sustained “injury to widespread brain networks without an associated history of head trauma.”

The report offers the first medical glimpse of the victims—US government personnel and their families who were serving on diplomatic assignment in Havana. From late 2016 to August 2017, they reported experiencing bizarre and inexplicable sonic and sensory episodes. The episodes tended to include directional, irritating sounds, such as buzzing and piercing squeals, as well as pressure and vibrations. Afterward, the victims developed a constellation of neurological symptoms.

In clinical evaluations of 21 of 24 individuals affected, an interdisciplinary team of doctors at University of Pennsylvania’s Perelman School of Medicine retrospectively pieced together symptoms—an average of 203 days after individuals were exposed. They found that the most common issues persisting more than three months after exposure were cognitive impairment (17/21); balance issues (15/21); visual (18/21) and hearing (15/21) problems; sleep impairment (18/21); and headaches (16/21).

More specifically, individuals had difficulty remembering things (17/21), reported feeling more emotional (11/21), had trouble getting their eyes to work together to focus on nearby objects (convergence insufficiency) (11/21), were sensitive to sounds (14/21), developed headaches while trying to work (16), and had trouble maintaining a static posture while at rest (16).

The doctors developed individualized rehabilitation programs for 18 individuals. While the doctors noted improvement from those efforts, 14 individuals with the most severe symptoms had not returned to work at the time of evaluations.

Like a concussion, but without the head blow

In their analysis, published late Wednesday in JAMA, the doctors note that the array of symptoms is similar to that of concussion or mild traumatic brain injury. However, the individuals reported no physical head trauma, and conventional magnetic resonance imaging (MRI) revealed no clear structural injuries. All brain imaging showed normal or nonspecific issues that may be explained by age or preexisting issues, despite earlier reports.

While the doctors went into more detail—at least as much detail as they could—they didn’t offer any hypotheses as to what could have caused the injuries. Thus, the report is unlikely to curb wild speculation on the incidents.

Since initial media and government reports of the cases appeared last year, guesses about the cause of the experiences and symptoms have swirled. Some suggested cloak-and-dagger scenarios of malfunctioning surveillance equipment or the trial of a covert sonic weapon wielded by a hostile foreign power. Health pundits discussed the possibility of a virus, a chemical agent, or mass psychogenic illness (MPI)—essentially a collective delusion among a cohesive group of people that a sickness is spreading among them.

A panel of Cuban scientists—who did not have access to affected individuals’ medical reports—concluded in December that MPI was the most likely cause of the diplomats' situation, as reported by Science . They had examined the hearing of neighbors of US diplomats, plus assessed environmental sounds. The chirp frequency of the Jamaican field cricket (Gryllus assimilis) matches that of a grating sound on a recording of one of the attacks , they noted.

But the team of Penn doctors cast doubt on this hypothesis, noting that some of their clinical results—such as those on eye-movement exams—could not be consciously or unconsciously manipulated. They also note that MPI usually involves short-term health issues, whereas many issues experienced by the individuals studied had long-term impairments. Lastly, the 21 individuals do not all know one another, according to an accompanying report in JAMA.

The doctors were also skeptical that a virus or chemical agent could explain the cases. None of the individuals reported common infection symptoms, such as fever. And it’s unclear how a chemical could affect the brain but no other organ.

Last, the doctors noted that “it is currently unclear if or how the noise is related to the reported symptoms.” Sound in the audible range (20Hz to 20,000Hz) is not known to cause persistent central nervous system injuries, they note. They suggest that the sounds were merely associated with the actual harmful phenomena.

In an accompanying editorial in JAMA, neurologists Christopher Muth and Steven Lewis note that high-intensity, focused ultrasounds (>20,000Hz) can induce heating and brain tissue damage. “However, the technical challenges in using ultrasound waves for nonlethal attacks include the rapid absorption of ultrasound by surrounding air and a requirement for close proximity to the source to induce injury,” they write.

Likewise, researchers have found that infrasound can cause brain damage in rats, but again it would be technically challenging to pull off an attack without victims noticing massive speakers or other signs.

Call for caution

Overall, Muth and Lewis urged caution in trying to interpret the clinical results reported by the Penn doctors. They note that many of the symptoms are self-reported and there was an average of 203 days since the exposures. Doctors don’t have baseline health data on those individuals, either. And lastly, basic data on individuals, such as age, were withheld for security reasons. Penn doctors could only report average age of the 21 individuals (43 years) and the gender breakdown (11 women and 10 men).

The lead Penn doctor told JAMA that the doctors involved in the evaluations had all signed a non-disclosure agreement with the State Department, so they cannot discuss whether they know more about the attacks.

These issues make it difficult to interpret the data, Muth and Lewis argue. For instance, three of the individuals needed hearing aids after being evaluated. But without knowing their age and hearing ability prior to the exposure, it’s difficult to say if this is concerning.

“At this point, a unifying explanation for the symptoms experienced by the US government officials described in this case series remains elusive and the effect of possible exposure to audible phenomena is unclear,” they conclude.

Muth and Lewis call for more testing and evaluation of the individuals, which Penn researchers are already doing. This includes more advanced imaging to assess possible structural abnormalities. Muth and Lewis also recommended that embassy staff in Havana undergo baseline neurological testing, in case there are future attacks. That way, doctors could pinpoint effects of the attacks while factoring out existing issues.

For now, the US embassy is staffed with a skeleton crew, performing only essential functions. The State Department has issued a Level 3 travel advisory, stating “because our personnel's safety is at risk, and we are unable to identify the source of the attacks, we believe US citizens may also be at risk.”

JAMA, 2018. DOI: 10.1001/jama.2018.1742 (About DOIs).