As of August 10, the U.S. Centers for Disease Control and Prevention (CDC) is reporting human cases of influenza A (H3N2) variant (H3N2v) in 4 states. To date, all of the reported cases of the H3N2v virus are similar to the 13 H3N2v viruses identified during July 2011–April 2012. All sequenced viruses had acquired the M gene from the influenza A (H1N1)pdm09 virus.
According to the official CDC data, from July 12 to August 9, a total of 153 cases of H3N2v infections were reported in Indiana (120 cases), Ohio (31), Hawaii (one), and Illinois (one). Of the 138 reported cases for which demographic information was available, 128 (93%) occurred in persons aged <18 years, and 10 (7%) occurred in adults. The median age of patients was 7 years. Two persons were hospitalized as a result of their illness; no deaths occurred. The patient in Hawaii was exposed to swine on the job, and no additional cases were found in Hawaii. The 152 patients reported from Illinois, Indiana, and Ohio resided in 27 counties; all reported direct or indirect exposure to swine, the majority at agricultural fairs. There have been no reports of human to human transmission thus far during this outbreak although a limited number of cases were reported in 2011.
The dramatic increase in the number of cases reported is due, in part, to a change in the way cases are “confirmed” positive for reporting purposes. The CDC recently updated the results interpretation of a diagnostic test used by public health laboratories and began classifying those H3N2v presumptive positives as confirmed positives.
Additional information is available on the CDC website and Dr. Jennifer Koeman, National Pork Board Director of Producer and Public Health, has compiled a list of influenza-related resource materials on the Pork.org website as well.