If you or those
close to you suffer from asthma attacks you will be interested in the scientific
link between the dust in the environment and your health. In this week’s edition
of Cleaning Up The Mess, eco-toxicologist, UWI lecturer Dr Azad Mohammed and Dr
Marissa Gowrie, who have worked jointly on a research programme on the magnitude
and impact of Saharan dust in the Caribbean are our joint guest columnists on
Cleaning Up The Mess.
Every year from February to
October, our blue skies periodically disappear behind a blanket of haze which
can be attributed to increased levels of Saharan dust in the atmosphere. For
those who suffer from asthma or other respiratory distress, it is also a sign to
restock the medicine cabinet with extra refills for antihistamines and inhalers.
It becomes entrenched in their daily routines, keys, lunch bag, hair brush, and
yes the inhaler. Just like we have grown accustomed to wet and dry seasons,
asthma sufferers have grown accustomed to the on and off season for symptoms.
The “on” season usually coincides
with the months from February to October, which represents the summer months in
the northern hemisphere and the period which signals the start of the migration
of Saharan dust from Africa, to the Americas. The migration of Saharan dust
begins when storms in North Africa lift Saharan sand and dust into the upper
atmosphere, where it is carried thousands of miles across the Atlantic
Ocean into the Caribbean and southern parts of the Atlantic US. Movement of the
clouds can be tracked using satellite imagery or by ground observations. Most
people only notice the dust clouds when it shrouds the sunset in a yellowish
haze and the hillsides disappear behind a blanket of haze.
Various studies have raised
concern about the potential link between the dust levels and the impact on human
health. Research which suggest that there may be a correlation between high
concentrations of particles less than 2.5µm (0.0025mm) in diameter (PM2.5) and
increases in emergency room admissions for respiratory and cardiovascular
disease have been reported in North America, Asia and Europe. The primary health
concern associated with Saharan dust is the particulate matter—microscopic dust
(less than the thickness of hair, < 2.5µm) which can sidestep the lungs’ natural
defences. These tiny particles can contribute to cardiovascular problems as well
as respiratory diseases such as asthma, especially in children.
Recent research by Dr Monteil in
Trinidad has shown that the symptoms of rhinitis in the student population
exceeded 30 per cent. The reasons for such high prevalence of allergic disease
in Caribbean youth remain obscure; however, preliminary data from Trinidad have
hinted at a higher prevalence of these disorders among students attending
schools in urban areas. In Barbados, studies have suggested that there was a
17-fold increase in the prevalence of asthma from 1973 to 1996, with acute
asthma attacks accounting for 22.3 per cent of the Queen Elizabeth Hospital
emergency room visits in 1999. This increase corresponded to the observed
increase in African dust flux affecting Barbados. The dust particles also serve
as a vehicle for the transport of known asthma triggers such as biological
materials including bacteria, viruses, fungal spores and pollen. They have also
been shown to transport various pollutants such as metals and pesticides.
To date, more than 200 species of
viable bacteria and fungi have been identified from air samples collected during
Saharan dust events in Trinidad and Tobago. However, there is still uncertainty
as to whether dust clouds could transport other asthma triggers such as pollen.
Recent research completed by Dr Marissa Gowrie of the University of the West
Indies has sought to provide some light on this issue.
Dr Gowrie collected air samples for pollen enumeration over a two year period at
Galera point, Toco, and at the University of the West Indies (UWI), St
Augustine. This sampling covered both dust and non-dust periods over the two
years. Data for other environmental triggers for asthma: Rainfall, relative
humidity, temperature, barometric pressure and Saharan dust were also collected.
This data was then correlated with
paediatric asthma admissions (children 15 years and younger) at the Accident and
Emergency Unit of the Eric Williams Medical Sciences Complex (EWMSC) to help
develop a predictive model of asthma incidences. Dr Gowrie found that very
little African pollen is transported on these Saharan dust clouds. However, the
studies did suggest that local pollen in the presence of other factors such as
dust concentrations, relative humidity, wind speed and temperature variations
contributed to increases in paediatric asthma. A predictive model based on the
interactions of these factors was created, which is able to forecast paediatric
asthma admissions for 84.7 per cent of the asthma cases studied over the two
A key component of
the model was the inclusion of lag time which took into account the incubation
time before the onset of asthma symptoms. The model is able to forecast
paediatric asthma a week in advance, using asthma admissions from three days
prior. It showed that asthma increases when there is a certain combination of
factors, specifically days of high pollen, high dust, high wind speed, and high
temperature variations, coupled with two consecutive days of high relative
humidity. Next week, look out for a special environmental series with guest
columnist Dr Roodal Moonilal, Minister of Housing and the Environment.