Diplomats in Cuba have reported mysterious symptoms.

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Diplomats reported these symptoms starting in 2016. Getty Images

More than 30 Americans and Canadians in Cuba have reported brain injuries that may be the result of an attack with an unknown device.

Last week another Canadian diplomat stationed in Cuba reported a mysterious concussion-like illness. This brings to 13 the total number of Canadian diplomats or family members affected by “unusual health symptoms.”

More than 20 American diplomats and dependents have also been affected over the past two years.

Most were stationed in Cuba, leading some to call this the “Havana syndrome.” One American government official, though, reported falling ill while in Guangzhou, China.

The cause of the illnesses is not clear, but the CBC reports that both the U.S. and Canadian governments believe that diplomats were attacked by unknown technology.

Doctors at universities in the U.S. and Canada continue to investigate these cases in an attempt to determine what’s behind the symptoms and how best to treat the people affected.

Sufferers reported hearing sounds that include “buzzing,” “grinding metal,” “piercing squeals,” and “humming,” according to a study published in JAMA in March.

For some, the sounds were associated with a feeling of pressure or vibration, like “air ‘baffling’ inside a moving car with the windows partially rolled down,” wrote the authors.

People described the sounds and sensations as appearing to come from a distinct direction. They were also localized — when people changed locations the “sensation disappeared and the associated symptoms reduced.”

Almost all of the people reported the immediate onset of neurological symptoms such as feeling disoriented or agitated, nausea and dizziness.

Some people have also experienced ongoing symptoms, including memory problems, difficulty thinking or focusing, irritability and nervousness.

The authors of the JAMA paper described the symptoms as similar to a mild traumatic brain injury, or concussion — without any signs of physical trauma.

Right now, though, no one knows for certain what is behind this illness, and the U.S. and Canadian governments have yet to settle on an explanation.

Early on, the auditory phenomena prompted people to speculate that this was the result of a “sonic attack,” possibly using ultrasound or infrasound.

In March, computer science and engineering researchers at the University of Michigan proposed that a “poorly engineered ultrasonic transmitter” used to eavesdrop could potentially create the sounds heard by the people affected.

Some experts, though, say that the most likely explanation, given the sounds and symptoms, is exposure to radiofrequency/microwave radiation.

This type of radiation is produced by many devices, including radios, cellular phones, microwave ovens, radar transmitters and industrial equipment. Other unknown devices may be involved in these incidents.

Dr. Beatrice Golomb, a professor of medicine at the University of California, San Diego, laid out evidence in the journal Neural Computation in support of radiofrequency/microwave radiation as the culprit.

In an interview with Healthline, she said the sounds fit with what’s known as the “microwave auditory effect,” in which microwaves interact with the head to cause people to hear sounds.

Other characteristics of the sounds also point to this explanation, such as the localization of the sounds, the sound not decreasing when people covered their ears, and other people in the immediate vicinity not hearing any noise.

Golomb said even the physical and neurological symptoms fit with reports of health effects experienced by people exposed to radiofrequency/microwave radiation, including “from commercially acceptable levels of radiation.”

Dr. Douglas H. Smith, lead author of the JAMA study told the New York Times in September that microwaves are now considered a “main suspect.”

His team also thinks that people affected have suffered brain injury. Additional brain imaging is being done to determine the extent of the injuries.

The CBC reports that the U.S. and Canadian governments believe that these cases are the result of deliberate and targeted attacks. Potential suspects include other governments or individuals with backing from those governments.

Golomb said these may not necessarily be attacks meant to harm people, but could be a byproduct of a surveillance device. This type of surveillance was suspected in the microwaving of the U.S. embassy in Moscow during the 1960s and 70s.

The U.S. and Canadian governments continue to investigate these incidents. Finding the cause of the illnesses could help prevent future “attacks” and may help doctors treat those who are affected.

More than 33 American and Canadian diplomats and their families stationed in Cuba have reported a mysterious concussion-like illness over the past two years.

People experienced buzzing, humming and other sounds, followed by neurological symptoms such as feeling disoriented, dizziness and difficulty thinking and focusing.

Exposure to radiofrequency/microwave radiation is a main suspect behind these illnesses, either due to a targeted attack or as side effects of a surveillance device.