People ill with the novel influenza A (H1N1) virus infection may also have neurological problems, including seizures or altered mental state. While these symptoms have also been linked to seasonal influenza strains, this is the first report that the new virus can also trigger these complications.
The association between neurological problems and the virus emerged after four patients — all under age 18 — were admitted to University of Texas Southwestern Medical Center and H1N1 viral infection was confirmed. Two children had unexplained seizures within days of upper respiratory tract symptoms and the other two had disorientation and malaise, with slowed thinking and behavior.
The data, published in the CDC's July 24 Morbidity and Mortality Weekly Report, described the four cases of young people between 7 and 17 who were admitted to the hospital. They were each confirmed to have H1N1 virus infection, and the neurological symptoms were confirmed by brain scans and a complete examination by a neurologist. All of the symptoms resolved.
Between April 22 and July 20, the Dallas County Department of Health and Human Services identified 405 people with H1N1 and 145 of them were under 18. Of the 44 patients hospitalized with the virus, 26 were children.
Tim Uyeki, MD, a medical epidemiologist and deputy chief of the CDC Epidemiology and Prevention Branch, Influenza Division, said: “We should expect more cases to occur, including more severe neurological complications and perhaps even fatal outcomes.”
He noted that seizures and other neurological symptoms have been reported with seasonal influenza, and that the symptoms reported in these new cases are not as severe as some cases that have been identified in patients with seasonal influenza. And although complications such as encephalitis and seizures are rare, clinicians should be aware that they can occur with novel H1N1. In suspected cases of H1N1, physicians should prescribe antiviral medicines — oseltamivir or zanamivir — as soon as possible; it is unknown, however, if this treatment will alter neurological complications.
There is no evidence that the virus seeps into the brain. In fact, CSF samples taken from patients with H1N1 virus infection and neurological manifestations have turned up negative. Dr. Uyeki said that for severely ill seasonal influenza patients with encephalopathy or evidence of encephalitis, it has been hypothesized that the respiratory tract infection triggers immune system cytokines that result, in rare instances, in an inflammatory process in the brain, which can lead to neurologic sequelae or fatal outcomes.
• Centers for Disease Control and Prevention. MMWR Morb Mortal Wkly Rep 2009. Neurologic complications associated with novel influenza A (H1N1) virus infection in children –Dallas, Texas, May 2009; 58(28):773–778.