Thursday, January 31, 2013

Influenza Transmission, PPEs & `Super Emitters’

 

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Photo Credit PHIL (Public Health Image Library)

 

# 6898

 

Ideally, the well-protected HCW (Health Care Worker) working in an infectious environment would be wearing an N95 mask, gloves, gown and eye protection – what are collectively known as  PPEs or Personal Protective Equipment.

 

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But during the opening months of the 2009 pandemic, it became apparent that our world faced a serious shortage of PPEs, and so strategies were adopted to maximize their use.

 

In some cases nurses were issued only one N95 mask to be used for an entire 8 hour shift, while in other venues, HCWs were issued surgical masks in lieu of N95s, despite the recommendation at the time from the CDC that N95 masks were the preferred level of protection when caring for influenza patients.

 

These policies led to a number of complaints (see Nurses Protest Lack Of PPE’s , Report: Nurses File Complaint Over Lack Of PPE), as the debate over appropriate PPEs for pandemic influenza dragged on (see NEJM Perspective: Respiratory Protection For HCWs).

 

In June of 2010, the CDC proposed new guidance that relaxed those recommendations to using surgical masks for routine care, and reserving N95 masks for aerosol producing procedures (intubation, suctioning, etc).

 

Today, from the IDSA Journal of Infectious Diseases, we get a new study that casts doubts over the effectiveness of those revised PPE protocols. 

 

The paper is called:

 

Exposure to Influenza Virus Aerosols During Routine Patient Care

Werner E. Bischoff1, Katrina Swett3, Iris Leng3 and Timothy R. Peters2

Background. Defining dispersal of influenza virus via aerosol is essential for the development of prevention measures.

 

Methods. During the 2010–2011 influenza season, subjects with influenza-like illness were enrolled in an emergency department and throughout a tertiary care hospital, nasopharyngeal swab specimens were obtained, and symptom severity, treatment, and medical history were recorded. Quantitative impaction air samples were taken not ≤0.305 m (1 foot), 0.914 m (3 feet), and 1.829 m (6 feet) from the patient's head during routine care. Influenza virus was detected by rapid test and polymerase chain reaction.

 

<SNIP  Results>

 

Conclusions. HCPs within 1.829 m of patients with influenza could be exposed to infectious doses of influenza virus, primarily in small-particle aerosols. This finding questions the current paradigm of localized droplet transmission during non–aerosol-generating procedures.

 

(Continue . . . )

 

An accompanying editorial by Caroline Breese Hall is available at InfluenzaVirus: Here, There, Especially Air?.  Both, alas, are behind pay walls.

 

Fortunately we have a fairly detailed press release to look at, which summarizes the key findings thusly.

 

1) Researchers found that patients with influenza can emit small, influenza virus-containing particles into the surrounding air during routine patient care, potentially exposing health care providers to influenza virus up to 6 feet away from infected patients.

 

2) Five patients (19 percent) in study were "super-emitters" who emitted up to 32 times more virus than others. Patients who emit a higher concentration of influenza virus also reported greater severity of illness.

 

3) The findings suggest that more research on how influenza is transmitted is needed and that current influenza infection control recommendations for health providers may need to be reevaluated.

 

I’ve a few excerpts from the press release below, but follow the link to read it in its entirety.

 

Infectious Diseases Society of America

Patients can emit small, influenza-containing particles into the air during routine care

[EMBARGOED FOR JAN. 31, 2013] A new study suggests that patients with influenza can emit small virus-containing particles into the surrounding air during routine patient care, potentially exposing health care providers to influenza. Published in The Journal of Infectious Diseases, the findings raise the possibility that current influenza infection control recommendations may not always be adequate to protect providers from influenza during routine patient care in hospitals.

 

Werner E. Bischoff, MD, PhD, and colleagues from the Wake Forest School of Medicine in North Carolina screened 94 patients for flu-like symptoms during the 2010-2011 influenza season. Study participants had been admitted to the emergency department (52 patients) or an inpatient care unit (42 patients) of Wake Forest Baptist Medical Center, where vaccination for influenza is mandatory for health care providers.

 

Nasopharyngeal swabs were collected from each patient. Samples were analyzed by rapid testing and by PCR analysis. Air samples were obtained by placing three six-stage air samplers from within 1 foot, 3 feet, and 6 feet of patients. No aerosol-generating procedures—such as bronchoscopy, sputum induction, intubation, or cardiopulmonary resuscitation—were conducted while air sampling took place. During air sampling, the number of patients' coughs and sneezes were counted and assessed for severity. Patients also completed a questionnaire at admission to report symptoms and the number of days they were sick.

 

Of the 94 patients enrolled, 61 patients (65 percent) tested positive for influenza virus. Twenty-six (43 percent) released influenza virus into the air. Five patients (19 percent) emitted up to 32 times more virus than others. This group of patients with influenza, described by the researchers as "super-emitters," suggested that some patients may be more likely to transmit influenza than others. High concentration of influenza virus released into the air was associated with high viral loads in nasopharyngeal samples. 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 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, Dr. 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 patient's 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.

(Continue . . . )

 

The discovery of `super-emitters’ of influenza isn’t a complete surprise, as we’ve seen evidence of `super-spreaders’ of other diseases.

 

In fact, in epidemiology, there is a concept known as the 20/80 rule – that suggests that 20% of the host population contributes to 80% of the spread of a disease.

 

The most infamous super spreader was Typhoid Mary (Mary Mallon) who was an asymptomatic cook who spread the disease to scores of people early in the last century, and who spent much of her life in quarantine.


The concept of super-spreaders made headlines again during the SARS epidemic, where a handful of infected individuals appeared to cause an inordinately high number of secondary cases (see MMWR Severe Acute Respiratory Syndrome --- Singapore, 2003).

 

Despite decades of research, our knowledge of how influenza spreads, and what barriers work well to protect HCWs, remains limited.

 

But today’s study isn’t the first study suggesting a greater role in the aerosolized transmission of influenza (as opposed to large-droplet transmission).

 

In November of 2010, in Study: Aerosolized Transmission Of Influenza, we saw a report on the nosocomial spread of influenza believed to be caused by infectious aerosols spread by an imbalanced indoor airflow.

 

Another study (see Study: Aerosolized Influenza And PPEs) from March of 2012, looked at the effectiveness of various types of PPEs.

 

Researchers simulated the aerosolization of influenza viruses and measured the protective qualities of surgical masks and respirators by constructing a simulated  exam room using `coughing and breathing manikins’.


The major findings:

A surgical mask, as normally worn by HCWs, only blocked 56.6% of infectious virus particles.

 

But . . . if you tightly seal the surgical mask against the face , you can achieve a level of protection approaching that of a well fitted N95 respirator (94.8% versus 99.6%).

 

And a poorly fitted N-95 respirator provided little more protection (66.5%) than a loosely fitted surgical mask.


A few other relevant studies we’ve looked at previously include:

 

PPEs & Transocular Influenza Transmission
Study: Longevity Of Viruses On PPEs
IOM: PPEs For HCWs 2010 Update

 


Complicating matters immensely, while our Strategic National Stockpile contains more than 100 million  N95 and surgical masks (see Caught With Our Masks Down), the demand for PPEs during a serious pandemic would far exceed the supply. 

 

At one time the HHS estimated the nation would need 30 billion masks (27 billion surgical, 5 Billion N95) to deal with a major pandemic (see Time Magazine A New Pandemic Fear: A Shortage of Surgical Masks).

 

Which means that during a global pandemic – when the demand for PPEs will skyrocket – we run the risk of being caught with our masks down again.

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