Why do the different types of flu transmission matter, and how can New Jersey’s approach toward tuberculosis be instructive as experts suggest a possible H1N1 rebound on the horizon?

I was sitting in the airport and anxious to get home. The day before, I had finished my presentation at the National Air Filtration Association (NAFA) annual tech seminar titled, “The Perfect Storm.” I had talked about the convergence of events in the world today that seemed to be leading us towards a microbial disaster. Topics such as drug resistance, bio-terror, emerging new diseases, old diseases like tuberculosis, and the struggling global economy were discussed. Now I was ready to forget about it all and relax.

With a little bit of time before the plane left I decided to check my e-mail one last time. And there in the subject line it read “Eight swine flu cases identified in U.S.” It went on to talk about hundreds sickened in Mexico, and perhaps as many as 60 dead! My mind started to race. Was it a false alarm like the swine flu scare of the ’70s? Was this a deadly outbreak like the one in 1918? How fast would it spread? How far? How deadly would it become? Were we ready?

Well, it didn’t take long to answer my questions. As I am writing this, a little over six weeks have passed, and we have gone from the first eight cases in the U.S. to over 20,000 confirmed cases. It has been estimated by the CDC that there are actually several hundred thousand unconfirmed cases nationwide.

While we seem ready, many vulnerabilities have been exposed; thankfully, the severity of the symptoms of the disease seem to be mostly mild. Medical experts are nevertheless worried that the disease may mutate and come back with a vengeance in the fall, so preparations continue. An article in the New York Times talked about how hospital emergency rooms that normally see 200 patients a day were seeing upwards of 2,000 patients a day. It was becoming evident that as concern for this new strain of the flu reached a fever pitch, the potential existed for our emergency rooms to be overrun and overwhelmed. One New York City hospital even had plans to open an old emergency department and use it only for patients with flu-like symptoms.

It was becoming apparent that in order to keep our emergency response network focused on true emergencies, most of the influenza patients would have to be seen in clinics or doctors’ offices. This raised the question of what could be done to protect staff, other non-flu patients, and those there in a supporting role (family, friends, etc) from also contracting the flu in these settings. To provide an answer, we first must understand how the flu is transmitted.

Transmission Of Influenza

The three primary modes of flu transmission are large droplet transmission, contact transmission, and airborne or aerosol transmission. In the past, the medical community has emphasized large droplet as the primary mode of influenza transmission while downplaying the role of aerosol transmission. The control measures recommended for these applications have been based on the large droplet transmission theory. One document that has recently been published reflects a shift of thought by the American medical community on this issue.

In the November 2006 issue of Emerging Infectious Diseases, published monthly by the CDC, Dr. Raymond Tellier of the Hospital for Sick Children in Toronto, has published a paper titled, “Review of Aerosol Transmission of Influenza A Virus.” In his paper, Dr. Tellier states, “Published evidence indicates that aerosol transmission of influenza can be an important mode of transmission (that has) obvious implications for pandemic influenza planning.”

Dr. Tellier presents both epidemiologic observations as well as laboratory animal experiments as supporting the importance of aerosol transmission of influenza. He writes, “Despite the evidence cited in support of aerosol transmission, many guidelines or review articles nevertheless routinely state that ‘large droplet transmission is thought to be the main mode of influenza transmission.’” He adds, “… despite extensive searches, I have not found a study that proves the notion that large droplets transmission is predominant and that aerosol transmission is negligible (or nonexistent).”

Dr. Tellier points out that U.S. and Canadian pandemic influenza plans recommend surgical masks, not N95 respirators as part of personal protective equipment for routine patient care and that, “this position contradicts the knowledge on influenza virus transmission accumulated in the past several decades.” In contrast, the World Health Organizations (WHO) current (April 2006) guidelines for avian influenza recommends “… the use of airborne precautions when possible, including the use of N95 respirators when entering patients’ rooms.”

Dr. Tellier’s article lays out an excellent argument supporting the need to stress the importance of aerosol transmission during influenza outbreaks. Facilities and governments should take this into consideration when planning their protective controls, whether they are administrative, engineering, or personal protection.

So if we indeed may face a resurgence of H1N1 flu in the fall, it is conceivable that health clinics nationwide could be seeing millions of potential flu victims in these settings. If this happens and it is possible that a primary mode of transmission is through the air, then what can we do reduce further transmission of the flu in these settings?

Lessons From Tuberculosis Control

Fortunately, we have had extensive experience with a similar matter. Tuberculosis is an infectious disease that is spread primarily through the airborne route. While the rates of tuberculosis (TB) are fairly low in the U.S., the high global numbers of TB have been cause for us to remain vigilant and to take aggressive steps to keep our rate of disease low.

The state of New Jersey has an aggressive program to reduce the rate of TB statewide that has been mostly successful in recent years. According to Tom Privett, TB program manager for the N.J. Department of Health, “one of the problems this success has created is an unfamiliarity of dealing with TB on the part of many physicians within the state.” This lack of experience dealing with TB could lead to a resurgence of the disease through mishandling of cases.

In an attempt to address this possibility, the state of N.J. has created regional chest clinics that specialize in TB so that experienced TB physicians will be located strategically throughout the state. There was not enough need to build a brand new facility in the southern region, so the state sought out existing space that could be transformed for this use.

After a long search for a desirable location in southern New Jersey, the state was contacted by Nancy Gerrity, the director of Public Health Nursing for the Camden County Department of Health. She made them aware of an underutilized ambulatory care clinic in Bellmawr, NJ, that may meet their needs. There were some challenges and concerns since the facility was not designed for this use. The clinic shared its building with the local public library and also shared space with Planned Parenthood services and a nutritional supplement program for women and children. They would need to ensure that safeguards were installed to protect their neighbors as well as the other clinic occupants from potential exposure to TB.

To provide the necessary protection, it was determined that two negative pressure exam rooms would be created for providing care to TB patients. Negative pressure is created by ensuring that more air is exhausted from a space than is supplied to that space. This pressure differential creates a draw of air into the room that dramatically reduces the potential for contaminated air to leave that room. The pressure differential is continually monitored by a room pressure device to ensure that the room is operating properly whenever it is being used for cases requiring isolation.

Due to the close proximity of the library to the health clinic, all air that is exhausted from the exam rooms is passed through HEPA filters prior to being exhausted out of the clinic. Factory-tested HEPA filters are used to ensure that the filters are operating at 99.99% against a 0.3 micron size challenge agent. The HEPA filters are installed in a well-sealed housing to ensure that no contaminated air can bypass the filter and be exhausted, untreated, to outside the clinic.

In addition to using these methods of control for exam rooms, it has become common practice to use the same control measures in waiting areas of both hospital emergency departments as well as chest clinics such as the one in Camden County. Most of us are painfully aware of how long the wait in these settings can be. The risk of spreading infectious disease through the air is typically increased as we spend more time in close proximity to those who are infected. This can make the clinic waiting area a hot zone for transmission of disease.


The use of air filtration and room pressure controls to convert existing medical clinic space into areas that can be used to treat patients with a potentially airborne infectious disease is a low-cost, high-impact control measure that has a proven track record of success and value. As we brace ourselves for the potential onslaught of influenza patients this fall, this is a time for creative application of proven technologies, allowing us to provide adequate controls while also being fiscally responsible.ES