CDC confirms flu with MRSA in Maryland cluster

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Mar 19, 2012 (CIDRAP News) – The Centers for Disease Control and Prevention (CDC) has confirmed reports from Maryland officials that a recent cluster of four severe influenza cases in the state involved a seasonal H3N2 strain, complicated in at least two cases by drug-resistant bacterial infections.

The case cluster in a rural community involved an 81-year-old woman and three of her adult children; the mother and two of her children died.

The CDC said genetic sequencing showed that the H3N2 strain in the cluster was more than 99% similar to other H3N2 isolates submitted by Maryland health officials this season.

Although full antigenic testing is pending, the viruses "are close to the H3N2 component of the 2011-2012 seasonal vaccine such that vaccination should offer protection against these viruses," the CDC said in a Mar 16 statement. Earlier, a local health official said that the elderly woman had received a seasonal flu vaccine but her children had not, according to previous reports.

The CDC also confirmed the state's earlier report that at least two of the cases involved co-infections with methicillin-resistant Staphylococcus aureus (MRSA).

Testing of the MRSA isolates is continuing, "but preliminary results indicate that some of the MRSA isolates from Maryland are pulsed-field types USA300," the CDC said. "Strains from the USA300 MRSA pulsed-field type can cause community MRSA infections including outbreaks of skin infections."

Staph co-infection with flu "is a potentially catastrophic complication of influenza that can progress rapidly to serious illness and death," the CDC noted.

USA300 is the most common type of community-associated MRSA in the United States, according to a March 2009 article in Morbidity and Mortality Weekly Report, the CDC's weekly bulletin. The strain has been associated with fatal illnesses such as necrotizing pneumonia and severe sepsis.

USA300 and similar strains produce toxins that lead to intense inflammation, according to a January 2010 perspective article in the Journal of Allergy and Clinical Immunology. The strain also produces other kinds of toxins, including a variant of the one that causes toxic shock syndrome (toxic shock syndrome 1), the article says.

See also:

March 9 CIDRAP News story on case cluster

Mar 6, 2009, MMWR article

January 2010 J Allergy Clin Immunol perspective abstract

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