The US government has withdrawn two more US workers from its embassy in Cuba following fresh accounts of bizarre noises followed by an array of symptoms consistent with mild traumatic head injuries, according to a series of reports from the Associated Press.

The two workers are considered “potentially new cases” in mysterious incidents plaguing Cuba and also workers in the US consulate in the Chinese city of Guangzhou, just northwest of Hong Kong.

The workers have been sent to the University of Pennsylvania for more neurological testing, where experts previously evaluated and treated 21 of the 24 confirmed US cases from Cuba and have begun evaluating workers evacuated from Guangzhou.

Prior to these new cases, US officials had said that the most recent suspicious incidents in Cuba occurred in August of 2017—suggesting that the incidents there may have stopped. But over the weekend, Cuban officials released a statement reporting that one of the two new potential cases, a female worker, reported health symptoms on May 29 and had heard unexplained sounds in her home two days earlier.

As in previous cases, Cuba said it sent investigators to try to track down the source of the noise and injuries but found nothing. The statement only discussed one of the two potential new cases, without explanation, the AP noted.

The statement went on:

Cuba has publicly and officially reiterated its willing to cooperate seriously in the joint search for answers, clarity and the solution of the alleged facts. The Ministry of Foreign Relations reiterates that no evidence of the alleged incidents has been presented, and maintains its unwavering commitment to cooperate with US authorities.

The US government has maintained a travel advisory to Cuba due to the unexplained incidents and is operating the embassy there on a skeleton staff.

Meanwhile, US officials have deployed a medical team and experts from the Centers for Disease Control and Prevention to screen workers at the consulate in Guangzhou. Of the approximate 170 workers there, around 150 requested screening and eight have been evacuated to the University of Pennsylvania for further testing.

On Friday, the US State Department issued a fresh health alert for workers there. The alert noted that the department had received confirmation of “a medical incident consistent with what other US government personnel experienced in Havana, Cuba.”

The alert went on to caution:

If you or members of your family experience any unusual, unexplained physical symptoms or events, auditory or sensory phenomena, or other health concerns, please contact your health care provider to determine whether a medical evaluation and/or treatment is advisable. Symptoms to be attentive for include dizziness, headaches, tinnitus, fatigue, cognitive issues, visual problems, ear complaints and hearing loss, and difficulty sleeping.

The State Department advised those affected not to try to find the source of the sound themselves but rather to try to get away from it and consult a medical professional as soon as possible.

An explanation for the health incidents—dubbed by the government as “health attacks” and “specific attacks”—remains elusive. Though early speculation spun wildly around the idea of a “sonic attack,” experts have been skeptical that various types of sound waves could explain the reported brain injuries.

Critics and conjecture

Others have questioned the injuries themselves. In recent letters published in Cortex and the Journal of Neurology, neurologists Sergio Della Sala and Robert McIntosh of the University of Edinburgh and Roberto Cubelli of the University of Trento in Italy questioned the methods and data reported by the team of doctors at the University of Pennsylvania who evaluated affected US personnel. In a report in JAMA, the Penn team had concluded that 21 of the 24 US workers affected in Cuba had “sustained injury to widespread brain networks without an associated history of head trauma.”

In their brief but harsh critiques, Della Sala, McIntosh, and Cubelli argue that the evidence for cognitive deficits in the US workers is weak and that the Penn medical team used subjective and inappropriate criteria for their assessment. Central to their criticism is that the Penn doctors used a score of 40percentile or above as a cutoff point for passing neurophysiological tests in evaluations of six of the 21 patients evaluated (eTable 2). The critics argue that the 5percentile is the standard and that the higher threshold would generate abundant false positives. (Three of the six patients had scores below the 5percentile on certain tests.)

The Penn doctors did not immediately respond when Ars reached out for comment. A spokesperson for Penn Medicine told The Washington Post last Friday that the doctors are working with the State Department to conduct evaluations on more personnel from Cuba and China and would no longer be available for interviews.

But on June 1, a lead doctor and author of the JAMA report, Douglas Smith, provided a response to the critique to Science News via email.

The outlet reported that Smith said:

[H]e and his colleagues have more data than were included in the study. “We note that interpretation of neuropsychological test results is somewhat more nuanced than a simple counting of scores that are lower than a conventional percentile cutoff point,” Smith wrote in an email. Instead, the researchers considered how much each person’s performance on a particular test differed from what is normal for the individual. In some cases, test scores in one aspect of brain function fell far below that person’s normal — down to the bottom 10 percent of the person’s average brain function. That low level of function counts as impairment, says Smith, who directs the Center for Brain Injury and Repair at the University of Pennsylvania’s medical school.

If Ars reaches Smith or another doctor from the team, this post will be updated.

Otherwise, experts have not questioned whether the US personnel in China and Cuba have experienced something. Some have speculated that infectious agents or toxins could be playing a role. In December, Science reported that a panel of Cuban scientists—who did not have access to the US personnel affected in the incidents—concluded that mass psychogenic illness (MPI) was the most likely explanation. MPI is essentially a collective delusion among a cohesive group that a sickness or ailment is spreading among them.

The Penn doctors expressed doubt on this hypothesis in their JAMA report, noting that the symptoms they saw couldn’t be consciously or subconsciously faked and that not all of the affected individuals knew each other. Other critics have suggested that such points are not enough to dismiss the possibility.

Alberto Espay, a professor of neurology at the University of Cincinnati, seemed to agree. He noted to the Post that the medical literature has long documented cases of similar health problems in clusters of people in stressful situations. "The symptoms are certainly very real and in no way fabricated. This is not a case of a bunch of people colluding to try to come up with some symptoms all together," he said. "We're baffled by this [JAMA] report."