Five Questions With: Dr. Michael Koster

Dr. Michael Koster, a pediatric infectious-diseases specialist and a hospitalist at Hasbro Children’s Hospital, is an assistant professor at the Warren Alpert Medical School of Brown University, where he performs resident education and training. 

Koster’s research interest is in clinical virology. He completed his pediatric infectious-diseases fellowship at Hasbro Children’s Hospital and has worked as a pediatric hospitalist at Landmark Hospital in Woonsocket.

Providence Business News asked Koster about a rare paralytic condition causing muscle weakness in the arms and legs caused by a viral infection, acute flaccid myelitis, which the Centers for Disease Control and Prevention has been monitoring closely since 2014. 

From August 2014 through October 2018, CDC has reported a total of 396 confirmed cases of AFM across the U.S.; most of the cases have occurred in children. As of Oct. 26, there were 72 confirmed cases of AFM so far in 2018. Rhode Island has had two confirmed cases of AFM; one in 2016 and one in 2018, according to the R.I. Department of Health.

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PBN: What is acute flaccid myelitis and why is it called that?

KOSTER: This is both the diagnosis as well as a descriptive name for the disease that causes muscle weakness – myelitis = muscles, flaccid = weak or poor tone, acute = is happening in a short time frame. The disease causes something like a molecular mimicry, which is when the body’s immune system responds to some kind of infection, [such as] an enterovirus, and then mistakes your own nervous tissue – spinal cord – as foreign or “disease.”

Our nerves are what control our muscles and this can lead to major muscle groups in the legs, arms and core depending on where the spinal cord is involved. Other smaller muscle groups, where the nerves come more directly from the brain – cranial nerves, can lead to difficulty with eye movements, eye opening, or swallowing and speaking.

PBN: The CDC says this condition is caused by a viral infection from enteroviruses, most likely coxsackievirus A16, EV-A71 and EV-D68, found in spinal fluid of affected patients since 2014. What is the most likely source for such viruses?

KOSTER: We still don’t know the cause of AFM exactly, as not all cases have identified an offending germ. What is clear is that several types of enteroviruses, as well as other infectious causes seem to trigger the immune system, which causes the clinical condition of AFM. For the vast majority of people who get infected with an enterovirus, the infection is a self-limited viral illness, [such as] a cold or stomach bug. Just to give an example of the statistics, about 5 million people in the U.S. will have an enteroviral infection; so far as of Dec 14, there [have been] 165 cases of AFM.

These viruses circulate in people as the source of infections to others, and can be isolated in our respiratory secretions, saliva and stool. They are typically spread through contact with infected items such as doorknobs, and then infecting oneself with dirty hands – fingers in mouth, nose, eyes, etc. There is no vector – [such as] a mosquito, tick, insect – but hard, nonporous surfaces and high-touch areas have the highest risk of being contaminated.

Our mothers and grandmothers were right when they told us to wash our hands. We also need to practice good hygiene around coughing, sneezing and health care professionals need to wear a mask, or stay home when symptomatic. It is very important to note that while the virus is contagious, the disease of AFM is not contagious, and AFM is likely the culmination of an offending infection combined with environmental and genetic predispositions.

PBN: So far, there have only been two reported cases of AFM in Rhode Island. Was there any common factor between the two that may help Rhode Islanders better protect themselves from the virus?


PBN: The CDC suggests a number of general hygienic steps similar to avoiding the flu. If you’re being diligent about flu this season, will that general preparedness be a good de facto defense against AFM?

KOSTER: Yes, these are the control and prevention measures that help with all respiratory illnesses, including influenza, RSV, parainfluenza, adenovirus, rhinovirus, human metapneumovirus, coronavirus, etc. While we certainly take this illnesses seriously and the CDC has also established a task force, the vast majority of people who get a viral respiratory illness, including enteroviral infections, are not going to be at risk for AFM.

PBN: What symptoms would indicate a possible AFM infection? What warning signs would distinguish a serious infection from the common flu?

KOSTER: Sudden muscle weakness is the hallmark of the disease, with difficulty walking, or holding something in your arm as a presenting sign.  Also, the small muscles that control facial expression, speaking and swallowing can be an initial sign. In almost all the cases, there is a preceding upper respiratory viral illness about two weeks before symptom onset, meaning that it is not concurrent with the viral illness, while fever, headache, muscle aches, fatigue, sneezing, coughing and sore throat are more consistent with an active flu or “flu-like” respiratory illness.

Rob Borkowski is a PBN staff writer. Email him at