Drug-Resistant Flu
The increase in amantadine- and rimantadine-resistant H3N2 influenza A viruses over the past decade is alarming, Rick A. Bright, Ph.D., of the Centers for Disease Control and Prevention, Atlanta, and his colleagues reported.
Between the 1994–1995 and 2003–2004 flu seasons, the proportion of resistant H3N2 viruses increased from 0.4% to 12.3%, a study of more than 7,000 influenza A field isolates showed. Most (84%) of the resistant viruses were isolated since the 2003 flu season, with 61% of those from people in Asia, the investigators found (Lancet 2005;366:1175–81).
Furthermore, between the 2003–2004 season and the first 6 months of the 2004–2005 season in the United States, resistance among comparable isolates increased from 2% to 15%.
The high incidence of drug-resistant H3N2 viruses circulating in regions that also have a high incidence of avian influenza (H5N1)—which is also resistant to amantadine and rimantadine—suggests that these drugs should be used with greater caution.
Pertussis Vaccination
A pertussis vaccine proved safe and effective in adolescents and adults in a recent study, and routine use in these populations might reduce overall disease burden and transmission to children, according to Joel I. Ward, M.D., of the University of California, Los Angeles, and his colleagues.
A total of 2,781 healthy people aged 15–65 years were randomized to receive an acellular pertussis vaccine (GlaxoSmithKline) or a control vaccine. The pertussis-antigen content in the pertussis vaccine was about one-third of that used in children. Primary infection occurred in one person in the pertussis vaccine group, and in nine people in the control vaccine group, for an overall adjusted vaccine efficacy of 92%. No vaccine-associated adverse events occurred (N. Engl. J. Med. 2005;353:1555–63).
Pertussis is difficult to diagnose in adolescents and adults, and the disease burden is underappreciated. The findings of this study suggest that the annual incidence of primary disease in this population in the United States is 370 cases per 100,000 persons aged 15–65 years, or nearly a million cases per year.
Because immunity to pertussis wanes, people immunized as children can become infected later in life. Thus pertussis control may depend on immunization of all adolescents and adults as well as children, the investigators concluded.
Community-Associated MRSA
Certain patient characteristics play a role in the extent of community-associated methicillin-resistant Staphylococcus aureus infection, a study suggests.
The investigators compared 586 patients with CA-MRSA skin and soft tissue infections and 65 patients with invasive disease. Those with invasive disease were significantly more likely to be smokers (odds ratio 2.18) or injection drug users (OR 5.56), or to report a history of underlying illness (OR 2.08), immunosuppressive therapy (OR 9.31), or emphysema or chronic obstructive pulmonary disease (OR 13.9), reported Jessica M. Buck, M.D., and her colleagues at the Minnesota Department of Health, Minneapolis (Emerg. Infect. Dis. 2005;11:1532–8).
Invasive disease isolates were significantly less likely to be susceptible to ciprofloxacin and clindamycin, and significantly more likely to have health care-associated subtypes, compared with the skin and soft tissue isolates. This suggests that patients with invasive disease may have had health care exposures that were not part of the exclusion criteria in the CA-MRSA case definition, and that some of the invasive infections classified as community acquired were actually health care acquired, which are typically resistant to more drugs.
Asthma and Metapneumovirus
The recently discovered human metapneumovirus may play a direct etiologic role in acute asthma exacerbations in adults, a prospective observational study suggests.
Seven of 101 adults hospitalized with an acute asthma exacerbation tested positive for hMPV. One of 75 patients who was also tested at 3-month follow-up had hMPV infection at that time, but none of the 7 who had hMPV infection at admission tested positive at follow-up, reported John V. Williams, M.D., of Vanderbilt University Medical Center, Nashville, and his colleagues (J. Infect. Dis. 2005;192:1149–53).
Previous studies have suggested a link between hMPV infection and acute asthma exacerbations in children, and between other respiratory viruses and exacerbations in children and adults, but this is the first to link hMPV infections with such exacerbations in adults, the investigators noted. Patient characteristics in this study suggest that more severe underlying disease confers greater risk, they added.