This year, more than half of all U.S. states have had confirmed or possible cases of acute flaccid myelitis, the polio-like illness that can cause paralysis and mostly affects children, according to an exclusive CNN analysis.
Of those, 62 cases of acute flaccid myelitis, or AFM, have been confirmed in 22 states, according to Nancy Messonnier, a top official at the Centers for Disease Control and Prevention.
CDC officials say some possible suspected causes, like polio and West Nile virus, have been ruled out.
Since the condition was first recognized by CDC in 2014, the agency has confirmed 362 cases.
Cases similar to Tunan's son are spreading to children around the age of four nationwide.
20, the CDC had confirmed 38 cases in 16 states, which aren't required to report AFM cases to the CDC.
The spikes were significantly higher in 2014, 2016 and 2018-to-date than in 2015 or 2017. "Right now, we know that poliovirus is not the cause of these AFM cases".
AFM may be caused by other viruses, including enterovirus, environmental toxins and a condition in which the body's immune system attacks and destroys tissue that it mistakes for foreign material, Messonnier said: "This is a mystery so far, and we haven't solved it yet, so we have to be thinking broadly". Another kind of virus was found in only some of the cases.
Symptoms of AFM include sudden limb weakness, loss of muscle tone and reflexes, facial and eyelid drooping, difficulty moving the eyes, difficulty swallowing and slurred speech, the CDC said.
Since officials have been unable so far to determine how the disease spreads, they are starting to count suspected cases as well as confirmed to better anticipate increases in confirmed cases over the coming months, she said.
Some patients recover quickly, while others experience paralysis and require ongoing care.
The overall rate of AFM is fewer than one in a million, she said.
"We know this can be frightening for parents, and I know many parents want to know what signs and symptoms they should be looking out for in their children", she said.
Health officials call the condition acute flaccid myelitis (AFM).
Last year, one child died of the disease.
More broadly, she noted, "there is a lot we don't know about AFM". Also, she said there can be lags in reporting because of the time it takes to review a patient's clinical syndrome and radiographic findings.
The agency doesn't know who may be at higher risk for developing this condition or the reasons they may be at higher risk. No pathogen has been consistently detected in the patients' spinal fluid.
There is no specific treatment for AFM, but doctors may recommend physical or occupational therapy to help with arm or leg weakness. It's a rare disease, but the CDC thought that they might glean more about the nature of the outbreak, as well as clues about how to contain it, by releasing a report to the public.