Apr 9, 2010
Study suggests 'silent' flu spreaders less important than thought
The proportion of viral shedding from flu infections that are preclinical or asymptomatic may be less important in the spread of influenza than previously thought, according to a Hong Kong study published online today in the Journal of Infectious Diseases. The study is notable in that it included subjects with naturally acquired influenza A and B rather than experimental infections; volunteer challenge studies tend to include younger persons screened to ensure they do not have immunity to the strain being studied, so results may not be generalizable to the overall population. In the current study, 59 previously healthy people with laboratory-confirmed influenza were followed through the course of their illness to measure viral shedding by PCR testing. In patients with influenza A, viral shedding was highest during the first 2 to 3 days of clinical illness and then waned; shedding in influenza B was variable, with no peak apparent. The authors estimated that 1% to 8% of shedding occurred before symptom onset. Viral shedding was low in eight patients (14%) with confirmed illness but no clinical symptoms.
Apr 9 J Infect Dis article
Intradermal flu shot may be good alternative for older adults
Injecting influenza vaccine between layers of the skin rather than into the muscle may prove an effective alternative for healthy older adults, according to a study in Clinical Infectious Diseases. Researchers administered seasonal influenza vaccine in either a standard 15-microgram (mcg) dose or a lower, 9-mcg dose intramuscularly (IM), or a 9-mcg or two 4.5-mcg doses intradermally (ID) to 257 healthy volunteers. All the lower doses, whether IM or ID, produced similar immune responses to the full dose against seasonal H1N1 and H3N2 flu strains. And subsequent revaccination of the lower-dose recipients did not yield improved seroprotection rates. The ID vaccine, however, produced more local reactions of redness, swelling, and itching.
Apr 8 Clin Infect Dis study abstract
Cold fronts may predict H5N1 outbreaks in Europe
Winter outbreaks of H5N1 avian influenza in Europe tend to occur at the leading edge of cold fronts, according to a study in Public Library of Science (PLoS) Pathogens. Researchers determined that the disease outbreaks in the winter of 2005-06 were driven by movements of large flocks of wild waterfowl away from areas of frozen surface water toward areas of high temperatures from 32°F to 36°F (0°C to 2°C). Such areas tended to occur on the leading edge of cold fronts, where lakes and streams remained open. The resulting congregation of varied bird species created ideal conditions for H5N1 transmission and many confirmed outbreaks in wild birds in 2006. The researchers write, "Movements of cold weather fronts, and in particular the 0°C isotherm of maximum surface air temperature, can readily be anticipated by operational weather forecasts." Such forecasts, they recommend, should trigger increased H5N1 surveillance in such regions, especially in poultry-dense areas.
Apr 8 PLoS Pathog study
Public Library of Science press release