Patients who emitted more virus also reported greater severity of illness. The current belief is that influenza virus is spread primarily by large particles traveling up to a maximum of 3 feet to 6 feet from an infected person. Recommended precautions for health providers focus on preventing transmission by large droplets and following special instructions during aerosol-generating procedures. In this study, Bischoff and his team discovered that the majority of influenza virus in the air samples analyzed was found in small particles during non-aerosol-generating activities up to a 6-foot distance from the patients head, and that concentrations of virus decreased with distance.
The study addressed only the presence of influenza-containing particles near patients during routine care, not the actual transmission of influenza infection to others. As Bischoff, et al. CDC and WHO state that influenza virus transmission primarily occurs by large-particle respiratory droplets traveling within a short distance of the source and that such particles are blocked during encounters between patients and healthcare professionals HCPs by face masks worn by HCP.
During routine, non-aerosol-generating patient care, the current precautions recommend that providers wear a non-fitted face mask. The researchers add, "The size of airborne particles determines how influenza virus is transmitted. Notably, no aerosol-generating procedures were undertaken during air sampling.
The predominance of small particles has been reported previously, with influenza virus detected in the exhaled breath of 4 of 12 subjects 33 percent breathing normally. The effect of coughing was studied in 47 influenza viruspositive patients. The published data and our findings indicate that small particles carry the majority of influenza virus other than virus released during aerosol-generating procedures.
We consider it unlikely that, during routine care, influenza virus is transmitted solely by droplet-sized particles. These findings suggest that current infection control recommendations may need to be reevaluated, the study authors say. Another recent study suggests that people may more likely be exposed to the flu through airborne virus than previously thought, according to new research from the University of Maryland School of Public Health. The study also found that when flu patients wear a surgical mask, the release of virus in even the smallest airborne droplets can be significantly reduced.
Routes of flu transmission include: 1 direct or indirect e. The relative importance of these modes of influenza transmission has not been well understood, but is critical in devising effective interventions to protect healthcare workers and vulnerable people, such as infants and the elderly.
The Centers for Disease Control and Prevention CDC recommends that persons with influenza wear surgical masks to prevent transmission to susceptible individuals. Yet, this recommendation has been supported so far by only one study of mask impact on the containment of large droplet spray during influenza infection. Maryland's study is the first to provide data showing that using a surgical mask can reduce the release of even the smallest droplets containing infectious virus.
For this reason, healthcare facilities should put surgical masks on those suspected of having influenza, and individuals with influenza can protect their families by wearing a mask. They found that the fine particles had 8.
They also tested the airborne droplets for "culturable" virus and found that virus was not only abundant in some cases, but infectious. However, there was a big range of how many viruses people put into the air some were undetectable while others put out over , every 30 minutes. The researchers also tested the impact of wearing a surgical mask on the virus shedding into airborne droplets.
Wearing a surgical mask significantly decreased the presence of virus in airborne droplets from exhaled breath. There was a 2. As Milton, et al. These results suggest an important role for aerosols in transmission of influenza virus and that surgical facemasks worn by infected persons are potentially an effective means of limiting the spread of influenza. The researchers report that when study volunteers were not wearing surgical masks, they detected virus RNA in coarse particles exhaled by 43 percent and in fine particles exhaled by 92 percent of influenza patients.
Milton, et al. Johnson et al. We view results from Johnson et al and the present study as complementary. However, surgical masks are not as efficient at preventing release of very small particles. It is well known that surgical masks are not effective for preventing exposure to fine particles when worn as personal protection.
We had hypothesized that when used as source control, exhaled droplets might be large enough prior to evaporation to be effectively captured, primarily through impaction. This appears to be true for virus carried in coarse particles.
But the majority of virus in the exhaled aerosol appear to be in the fine fraction that is not well contained. Nevertheless, the overall 3. Compliance, however, would be a major limitation resulting in lower efficacy in real-world practice.
In one previous study by Lindsley et al. This observation, along with our observation that it was possible to recover culturable virus from the fine-particle fraction using our device demonstrates that humans generate infectious influenza aerosols in both coarse and fine particle fractions. This lends support to the hypothesis that aerosols may be a common pathway for influenza transmission among humans.
However, a clear test of the hypothesis requires intervention studies that can interrupt only one mode of transmission without interfering with others. In that aforementioned study, Lindsley and Blachere, et al. Subjects were recruited from patients presenting at a student health clinic with influenza-like symptoms. Nasopharyngeal swabs were collected from the volunteers and they were asked to cough three times into a spirometer.
For half of the subjects, viral plaque assays were performed on the nasopharyngeal swabs and cough aerosol samples to determine if viable virus was present. Fifty-eight subjects were tested, of whom 47 were positive for influenza virus by qPCR.
Influenza viral RNA was detected in coughs from 38 of these subjects 81 percent. Viable influenza virus was detected in the cough aerosols from 2 of 21 subjects with influenza.
The residual protein of high molecular weight was present in the form of a component having a sedimentation constant of about S, and hence a probable particle diameter of about 70 mmicro. The proportion of the 30 S component in allantoic fluid of chick embryos infected with the PR8 strain of influenza virus was found to be considerably less. The S and 30 S components of F 12 allantoic fluid were purified and separated by differential centrifugation.
Antigenic shift is a sudden change in antigenicity caused by the recombination of the influenza genome, which can occur when a cell becomes simultaneously infected by two different strains of type A influenza.
The unusually broad range of hosts susceptible to influenza A appears to increase the likelihood that this event will occur.
In particular, the mixing of strains that can infect birds, pigs, and humans is thought to be responsible for most antigenic shifts. Notably, in some parts of the world, humans live in close proximity to both swine and fowl, so that human strains and bird strains, may readily infect a pig at the same time, resulting in a unique virus.
New subtypes of influenza A develop abruptly and unpredictably so that scientists are unable to prepare vaccines in advance that are effective against them. Consequently, the emergence of a new subtype of the virus can cause a global pandemic in a very short amount of time. In addition to vaccines, a few other weapons have been designed to combat the flu.
The antiviral medications amantadine and rimantadine can help reduce severity of illness in individuals with influenza that begin utilizing the drugs within two days of the onset of symptoms. These drugs work by hindering the change in pH that is necessary for the flu virion to release its contents into the cytosol of a host cell. Two additional antiviral drugs, zanamavir and oseltamivir, are effective against both A and B types of influenza.
Instead of interfering with pH shifts, zanamavir and oseltamivir block the glycoprotein neuraminidase so that the release of new virus particles is inhibited and their spread is thwarted. It is important to note that antibiotics are not capable of fighting the influenza virus itself, but are sometimes given to patients with the flu to stem attacks of opportunistic microorganisms that are responsible for many influenza complications.
Though widespread familiarity with the flu makes it seem relatively benign to much of the general population, the virus can be devastating. In and , more than 20 million people died from a strain of the virus commonly known as the Spanish flu that circulated through almost all inhabited regions of the globe. Many other outbreaks have occurred since that time, though none have been as deadly.
Nevertheless, influenza together with complications of the virus is consistently among the top ten common causes of death in the United States, ranking higher than some other much more widely publicized killers, such as the HIV virus that causes AIDS. License Info. Image Use. Custom Photos. Site Info. Contact Us. The Galleries:.
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