Age between 2 and 4 years and the existence of an underlying neurologic or neuromuscular disease are independent risk factors for influenza-related neurologic complications in children, Dr. Jason G. Newland and his colleagues reported.
In a retrospective cohort study conducted from June 2000 to May 2004, Dr. Newland, then of the Children's Hospital of Philadelphia, and his colleagues analyzed 842 patients aged 1 week to 21 years with laboratory-confirmed influenza. Of these, 72 patients experienced an influenza-related neurologic complication, including seizures (56), encephalopathy (8), postinfectious encephalopathy (2), stroke secondary to hypotension (4), and aseptic meningitis (2).
In the study based on an analysis of nine contiguous zip codes surrounding the hospital, the investigators also concluded that the incidence of influenza-related neurologic complications is approximately 4 cases per 100,000 child-years in the United States (J. Pediatr. 2007;150:306–10).
Dr. Newland, now of Children's Mercy Hospital in Kansas City, Mo., and his colleagues used logistic regression to determine that being an age between 6 months and 4 years put patients at elevated risk for developing neurologic complications, with the greatest risk occurring between 2 and 4 years—with an odds ratio of 10.
In addition, compared with patients who did not have a history of a neurologic or neuromuscular disease (NNMD), children who had such a history (including febrile seizures, an incident of encephalopathy, or developmental delay) also were more likely to have a seizure or other complication during influenza infection, with an odds ratio of 6.6. Although not previously reported in association with influenza, this is not entirely unexpected because patients with an NNMD—especially those with a history of seizures—are likely to have seizures during an acute illness, the investigators said.
Neither influenza type nor season put patients at any increased risk for neurologic complications.
Dr. Newland and his associates' findings are in contrast to reports from Japanese investigators during the past decade about severe and frequent influenza encephalopathy—including fatal encephalopathy rates reported as high as 25%–37%—in that country. Only 1% of patients in this study were hospitalized with influenza, and no deaths were reported in the U.S. investigation.
Limitations of this study included the fact that the areas surrounding the hospital represent a predominantly African American population, “and so our findings may not be generalizable to the rest of the country.” Another is that, because influenza testing is typically performed only on patients with cough and rhinorrhea, infected patients who did not present this way may not have been diagnosed and, therefore, tallied. Also, “the definition of acute encephalopathy is somewhat arbitrary and may both under- and overidentify patients with the acute onset of neurologic symptoms,” they wrote.
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