Asthma In Urban Settings

 

Asthma is a disease that develops due to genetic and environmental factors.  Studies of have shown a dramatic increase in the prevalence of asthma over the past few decades (Crain).  The rates have been growing highest in urban settings (Etzel).  However, these observations cannot be accounted for by changes on the genetic level.  Therefore, many researchers have concluded that the bulk of the increase in asthma prevalence must be due to changes in environmental exposures.  Many studies that have attempted to describe asthma risk factors in urban areas have focused on outdoor air pollution, mainly due to increased traffic.  In fact, researchers have shown a correlation between increases in outdoor air pollution and increases in asthma (DÕAmato).  This is controversial, however, as many studies show no association between development of asthma and outdoor pollution.  Rather, these studies suggest that indoor pollution is responsible for the development of asthma in children and that outdoor pollution is only a trigger (Kunzil, Etzel, Hirsch).  In either scenario, asthma morbidity is on the rise and pollution appears to be the culprit.

 

Air pollution is also associated with a variety of other ailments.  These include colds, influenza, bronchitis, days of reduced activity and cardiovascular disease (Kunzil).

 

At Risk Populations:  Those individuals that are at risk of air pollution related asthma include the elderly, young children, chronic disease sufferers, and those predisposed to asthma.

 

Distribution:  Increased rates of asthma associated with air pollution tend to be high in Westernized/urbanized countries.  Countries with a high prevalence include Australia, New Zealand, United Kingdom and many countries of Eastern Europe (http://www.asthma.co.uk.org).

 

Mechanism:  A proposed mechanism by which air pollution initiates an asthma attack is through the creation of highly reactive oxidative molecules.  These oxidants aggravate the epithelium of the respiratory system and initiate an immune response.  The surrounding tissue becomes inflamed and the individuals experiences asthma symptoms (Lee). 

 

Interaction:  Research has shown that air pollution can interact with allergens (ragweed, animal dander) to intensify asthma symptoms.  It is believed that air pollutants act as a ÒprimerÓ that irritates the respiratory epithelium.  This allows for easier access by allergens to the epithelium and results in increased asthma symptoms (DÕAmato).          

 

Potential Causes:  Air pollution in urban areas can be created from a variety of sources.  These include power plants, industry, and even the home.  However, the main source of outdoor air pollution in cities is from traffic emissions.  The chemicals that are associated with Òtraffic emissionsÓ include:

 

 

A study of Korean children under 14 years old demonstrated that that each of these chemicals significantly increased the risk of hospitalization due to asthma attacks.  Each chemical, individually, was associated with a 10-15% increased risk of hospitalization.  One key item to note is that the concentration levels of each of these chemicals were monitored during the entire study.  These levels did not exceed the current maximum allowable levels in Korea (Lee).

 

Smog:  Smog formation due to increased traffic has become a problem for many cities.  In response to this, smog alert systems have been developed in order to inform communities about potential smog hazards.  These alerts are typically targeted to those considered high risk.

 

Other Potential Asthma Triggering Chemicals (Delfino):

 

[O2] [CO] [Diesel Exhaust Particulates (DEP)] [Acetaldehyde] [Acetone] [Formaldehyde] [Benzene] [1,3-Butadiene] [Chloromethane] [p-Dichlorobenzene] [Ethylbenzene] [Methylene chloride] [Styrene] [Tetrachloroethylene] [Toluene] [m,p-Xylene] [o-Xylene]                      

 

Effect of morbidity/mortality:  Epidemiological studies have been conducted to try to determine morbidity and mortality attributable to air pollution and asthma.  In two European studies 40,000 deaths were attributed to air pollution.  In addition, there were 500,000 asthma attacks and 16 million days of restricted activity attributed to air pollution (Kunzil).

 

Prevention:  The best method to avoid asthma attacks due to pollution is for:

An Unfortunate Example

During the collapse of the World Trade Center Towers on September 11, 2001, a large cloud of particulate matter was created.  One individual reported that the air was Òdarker than a sealed vault and thicker than pea soup.Ó  This dust cloud which spread over Manhattan and surrounding boroughs deposited:

 

 

All of these building components can cause eye irritation, rashes and upper respiratory distress.  It is also believed that long-term exposure to such items may cause lung cancer (1 case per 10,000 exposed) and other respiratory diseases.  Short-term exposure, as seen on September 11, may trigger severe asthma attacks (http://www.cdc.gov/mmrw).

 

WTC Cough:  In the months that followed, 332 firefighters who were exposed to the dust cloud after the collapse developed World Trade Center cough.  This was defined as a persistent and severe cough in which the firefighter had to take at least four weeks of medical leave.  In addition, these firefighters coughed up a dark sputum that was infiltrated with pebbles and particles.  Such instances have only been seen in occupational settings after decades of exposure, not after an exposure of a few hours.  Furthermore, 0 of the 202 firefighters not present at the collapse developed WTC cough (Prezant).

 

Airway Hyperreactivity:  In a study of September 11 rescue workers, it was observed that those who had the highest exposure levels to the particulate cloud were approximately 7 times (OR=6.8; 95%CI:1.8-25.2, p=0.004) more likely to have asthma like symptoms 6 months after the collapse.  This trend continued for an additional 3 months.

 

 

References

 

Crain E., Walter M., O'Connor G., Mitchell H., Gruchalla R., Kattan M., Malindzak G.,

Enright P., Evans III R., Morgan W., Stout J.  Home and allergic characteristics of children with asthma in seven U.S. urban communities and design of an environmental            intervention: the Inner-City Asthma Study.  Environmental Health Perspectives, Sept 2002; 110 i9 p939(7).

 

DÕAmato, G.  Outdoor Air Pollution, climate and allergic respiratory diseases: evidence of a link.  Clin Exp Allergy 2002; 32:1391-3

 

Delfino R., Gong Jr. H., Linn W., Pellizzari E., Hu Y. Asthma symptoms in Hispanic children and daily ambient exposures to toxic and criteria air pollutants.  Environmental Health Perspectives, April 2003; 111 i4 p647(10).

 

Etzel, R.  How Environmental Exposures Influence the Development and Exacerbation of

Asthma. 

 

Hirsch T., Weiland S., von Mutius E., Safeca A., Grafe H., Csaplovics E.,

Duhme H., Keil U., Leupold W.  Inner city air pollution and respiratory health and atopy in children.  Eur Respir J 1999; 14: 669Ð77

 

Kunzil N.,  Kaiser R., Medina S., Studnicka M., Chanel O., Filliger P., Herry M., Horvak Jr. F., Puybonnieux-Texier V., Quenel P., Schneider J., Seethaler R., Vergnaud J., Sommer H.  Public Health Impact of Outdoor and Traffic Related Air Pollution: A European Assessmnet.  Lancet 2000; 356: 795-800

 

Prezant D., Weiden M., Banauch G., McGuinness G., Rom W., Aldrich T., Kelly K.  Cough and Bronchial Responsiveness in Firefighters at the World Trade Center Site.  N Engl J Med 2002;  347, No. 11: 806-15