Influenza A incidence peaks during winter in temperate regions. The basis for this pronounced seasonality is not understood, nor is it well documented how influenza A transmission principally occurs. Previous studies indicate that relative humidity (RH) affects both influenza virus transmission (IVT) and influenza virus survival (IVS). Here, we reanalyze these data to explore the effects of absolute humidity on IVT and IVS. We find that absolute humidity (AH) constrains both transmission efficiency and IVS much more significantly than RH. In the studies presented, 50% of IVT variability and 90% of IVS variability are explained by AH, whereas, respectively, only 12% and 36% are explained by RH. In temperate regions, both outdoor and indoor AH possess a strong seasonal cycle that minimizes in winter. This seasonal cycle is consistent with a wintertime increase in IVS and IVT and may explain the seasonality of influenza. Thus, differences in AH provide a single, coherent, more physically sound explanation for the observed variability of IVS, IVT and influenza seasonality in temperate regions. This hypothesis can be further tested through future, additional laboratory, epidemiological and modeling studies.virus survival ͉ vapor pressure ͉ droplet nuclei ͉ aerosol T here are 4 suspected modes of influenza virus transmission (IVT) (1): (i) transmission through direct physical contact with an infected individual, (ii) transmission via intermediate, often inanimate, objects (i.e., fomites), (iii) transmission via droplets expelled from infected individuals (e.g., by sneezing or coughing) that deposit on nasal or oral mucosa of a susceptible individual, and (iv) airborne transmission via expelled particles Ͻ2.5 m in radius, which are referred to as droplet nuclei and remain suspended in air as aerosols for extended periods of time. The relative importance of these 4 transmission modes remains a subject of much debate (1-7).A recent laboratory experiment examining influenza A transmission among guinea pig hosts suggests that airborne transmission may indeed be an important mode of IVT (8). In this study, groups of 4 infected and 4 susceptible hosts were maintained in separate cages at different temperature and relative humidity (RH) conditions. Transmission rates, measured as the percentage of susceptible hosts infected, were found to increase at lower RH. Two hypotheses were proposed to explain this relationship (8): (i) virus-laden droplet nuclei are more efficiently produced at lower RH because of increased evaporation of expelled droplet particles, such that more virus remains airborne longer; (ii) influenza virus survival (IVS) increases as RH decreases, such that the airborne virus remains viable longer at lower RH.Heretofore, analyses of the effects of humidity on both IVS and IVT have focused on RH as the metric for air moisture. RH is the ratio of the actual water vapor pressure of the air to the equilibrium, or saturation, vapor pressure of the air. Because saturation vapor pressure increases exponentially as te...

Tai chi--moving for better balance, a falls-prevention program developed from a randomized controlled trial for community-based use, was evaluated with the re-aim framework in 6 community centers. The program had a 100% adoption rate and 87% reach into the target older adult population. All centers implemented the intervention with good fidelity, and participants showed significant improvements in health-related outcome measures. This evidence-based tai chi program is practical to disseminate and can be effectively implemented and maintained in community settings.

Alaska and Louisiana child injury deaths were mostly attributed to preventable violations of 10 child safety standards, most commonly the supervision standard. The methods in this report were useful in identifying target populations and causes of death, which can be used to plan and implement interventions to improve supervision of children.

Jointly, the Association for Professionals in Infection Control and Epidemiology (APIC), the Society for Healthcare Epidemiology of America (SHEA), the Infectious Diseases Society of America (IDSA), the Association of State and Territorial Health Officials (ASTHO), the Council of State and Territorial Epidemiologists (CSTE), Pediatric Infectious Diseases Society (PIDS), and the Centers for Disease Control and Prevention (CDC) propose a call to action to move toward the elimination of healthcare-associated infections (HAIs) by adapting the concept and plans used for the elimination of other diseases, including infections. Elimination, as defined for other infectious diseases, is the maximal reduction of “the incidence of infection caused by a specific agent in a defined geographical area as a result of deliberate efforts; continued measures to prevent reestablishment of transmission are required.” (p24) This definition has been useful for elimination efforts directed toward polio, tuberculosis, and syphilis and can be readily adapted to HAIs. Sustained elimination of HAIs can be based on this public health model of constant action and vigilance. Elimination will require the implementation of evidence-based practices, the alignment of financial incentives, the closing of knowledge gaps, and the acquisition of information to assess progress and to enable response to emerging threats. These efforts must be under-pinned by substantial research investments, the development of novel prevention tools, improved organizational and personal accountabilities, strong collaboration among a broad coalition of public and private stakeholders, and a clear national will to succeed in this arena.

Norwalk-like viruses (NLVs), or small round structured viruses, are known to cause acute gastroenteritis associated with eating contaminated shellfish. Between 1993 and 1996, three oyster-related gastroenteritis outbreaks attributed to NLV occurred in Louisiana. Intensive trace-back and environmental investigations revealed that the overboard disposal of sewage by oyster harvesters into oyster-bed waters was the most likely source of contamination in at least two of the outbreaks. The small infectious dose of NLV, the large quantity of virus particles in stool, and the ability of oysters to concentrate virus particles suggest that oyster-related outbreaks will continue unless strong control measures are established. Efforts to halt improper sewage disposal in oyster-harvesting waters, including overboard sewage discharge, must be undertaken if future outbreaks are to be prevented.