Role of Climate in Influenza Transmission Revealed
|Two types of environmental conditions—cold-dry and humid-rainy—are associated with seasonal influenza epidemics, according to an epidemiological study led by FIC researchers.
Two types of environmental conditions—cold-dry and humid-rainy—are associated with seasonal influenza epidemics, according to an epidemiological study led by researchers at the Fogarty International Center. The paper, published in PLoS Pathogens, presents a simple climate-based model that maps influenza activity globally and accounts for the diverse range of seasonal patterns observed across temperate, subtropical and tropical regions.
The findings could be used to improve existing current influenza transmission models and could help target surveillance efforts and optimize the timing of seasonal vaccine delivery, according to FIC researcher Dr. Cecile Viboud, who headed the study. “The model could have a broader application, encouraging researchers to analyze the association between climatic patterns and infectious disease across a wide range of diseases and latitudes,” she said.
Human influenza infections exhibit a strong seasonal cycle in temperate regions; laboratory experiments suggest that low specific humidity facilitates the airborne survival and transmission of the virus in temperate regions. Specific humidity is the ratio of water vapor to dry air in a particular body of air while relative humidity—commonly used in weather forecasts—is the amount of water vapor in the air relative to its capacity to hold water vapor and is primarily a function of temperature.
Data from animal studies indicate low temperature and humidity increase the duration of the virus’s reproduction and expulsion in infected organisms and virus stability in the environment, increasing the probability of transmission through coughing, sneezing or breathing. In contrast, high temperature seems to block airborne transmission.
Benefits of Quitting Smoking Outpace Risk of Modest Weight Gain
The improvement in cardiovascular health that results from quitting smoking far outweighs the limited risks to cardiovascular health from the modest amount of weight gained after quitting, reports an NIH-funded community study. The study found that former smokers without diabetes had about half as much risk of developing cardiovascular disease as current smokers; this risk level did not change when post-cessation weight gain was accounted for in the analysis.
This study is the first epidemiological effort to directly address the health impact of the weight gain that many people experience following smoking cessation. The findings were published in the Mar. 13 Journal of the American Medical Association.
“Our findings suggest that a modest weight gain, around 5 to 10 pounds, has a negligible effect on the net benefit of quitting smoking,” said study co-author Dr. Caroline Fox of NHLBI. “Being able to quantify to some degree the relationship between the benefits and side effects of smoking cessation can help in counseling those who have quit or are thinking about quitting.”
Daily-Use HIV Prevention Approaches Prove Ineffective Among Women
Three antiretroviral-based strategies intended to prevent HIV infection among women did not prove effective in a major clinical trial in Africa. For reasons that are unclear, a majority of study participants—particularly young, single women—were unable to use their assigned approaches daily as directed, according to findings presented Mar. 4 by one of the study’s co-leaders at the Conference on Retroviruses and Opportunistic Infections in Atlanta.
The Vaginal and Oral Interventions to Control the Epidemic (VOICE) study was designed to evaluate the safety and efficacy of three HIV prevention strategies compared to placebo. The trial tested an investigational vaginal gel containing the antiretroviral drug tenofovir, a pill form of tenofovir and a pill containing a combination of tenofovir and emtricitabine. The study was sponsored and largely funded by NIAID.
In the trial, the three strategies were tested among 5,029 sexually active women 18 to 45 years of age at 15 sites in South Africa, Uganda and Zimbabwe. Nearly half of the study participants were under age 25 and most were unmarried (79 percent).
Study results indicate that most VOICE participants did not adhere to the daily use schedule. Moreover, single women 25 years of age and younger were the least likely to use the investigational products and the most likely to become infected with HIV. —compiled by Carla Garnett