CHAPTER THREE
72.3 Asthma
In this study a statistically significant increase (p =0.034) in the prevalence of asthma for 2003 (8% or 13/173) compared with 1990 (4% or 8/179) was evident. In a New Zealand cohort study the prevalence of asthma in the same population was 9% at 9 years of age and 21 % at age 26, thus higher than for the current study, although New Zealand is considered less polluted than the Vaal Triangle and South Africa at large. The prevalence of asthma in the white South African adult (age 15+) population is 7% for men and 9% for women, thus an average of 8% (SADHS, 1998).
The prevalence of asthma differs between countries and even between cities in the same country. The highest prevalence was found in countries with low air pollution, and the lowest prevalence in countries with high levels of pollution. Intermediate prevalence of asthma was found in countries with high ozone levels (Beasley, et. al., 1998).
Large well-designed epidemiological studies failed to show an association between N02, PM10 and asthma (Brunekreef and Holgate, 2002; Zemp, et.
al., 1999; Ackermann-Liebrich, et. al., 1997). However, some recent studies found that 03 might play a role in the onset and aggravation of asthma (O'Neil, et al.,2003; Ramadour, etal., 2000).
Several risk factors have been identified for asthma in as many studies. Risk factors for asthma identified in the current study, using logistic regression were:
~ having been an ever-smoker and
~ having an allergy.
Also evident from the current study is the fact that statistically significant (p=0.02) more individuals with asthma have at least one parent who suffers from asthma as well.
Twenty five percent (4/16) of individuals in the current study who have at least one parent who has been diagnosed with asthma, have been diagnosed with asthma themselves, already by the age of 10 years old and these individuals are still suffering from asthma. It seems thus that if at least one of an individual's parents is suffering from asthma and that individual is prone to get asthma it would happen before the age.of 10 years old and will most probably continue into adult life. This confirms what was found in the Tucson study, namely that children with maternal asthma were more likely to have asthma and most children who will develop atopic asthma have their first symptoms during the first 6 years of life (Taussig, et. al., 2003; Holgate, 1997).
Asthma is considered an allergic disease and it is believed that up to about 60% of asthma cases might be attributed to being allergic. Sensitisation for asthma does not necessarily have to be early in life though (Sporik and Platts- Mills, 200t: Holgate, 1997).
Persistence of childhood asthma
Epidemiological studies have indicated that the persistence of childhood asthma into adulthood depends amongst others on early «3 years of age) onset and severity of symptoms (Horak, 2003; Sumer, 2004). These indications were largely confirmed in the current study.
It was found that 5 of the 6 individuals, who were diagnosed with asthma before the age of 3, still had asthma attacks during the year preceding the
2003 survey, while only 2 of the 6 individuals who were diagnosed between 4 and .10 years old still have asthma.
As far as severity is concerned, it was found in this study that of the 6 individuals hospitalised for asthma as children, 4 still have asthma. It was further found that of the 6 individuals who were on asthma medication during the 1990 survey, 4 were still on medication during the 2003 survey (3 of the hospitalised children plus one extra). However, according to the classification of severity of asthma (Lalloo, et. al. 2000), the current severity of asthma amongst the study population can be described as mild intermittent.
Kurukulaaratchy, et. al., (2003) investigated risk factors influencing the persistence of wheezing with an early (within first 4 years) onset, to the age of 10 years. A genetic tendency to be asthmatic and atopic, appeared to be a crucial factor. This finding confirmed what was found in another study on twins, namely that factors inherited dominated environmental influences in the development of asthma (Kurukulaaratchy, et. al. 2003).
Findings from the Swiss studies were that children with a family history of asthma, hay fever or eczema, had higher rates of respiratory and especially allergic symptoms than those without, which makes them a susceptible subgroup (Braun-Fahrlander, et. al., 1997).
72A Wheezing
In the current study, the prevalence of wheezing without a cold was 8%, which is the same as was found in the SAPALDIA study and considerably lower than what was found in the New Zealand study. Both these studies were conducted in countries with low air pollution levels. The majority (10/15 or 67%) of individuals in the current study reporting wheezing without a cold, were asthmatics. This confirms what was found in the Tucson study, namely that wheezing without a cold could be used as a marker in an asthma predictive index (Taussig, et. al. 2003).
72.5 Lung functions
The New Zealand study by Sears and co-workers suggested that impaired lung functions found in adults with respiratory diseases already occurred in early childhood (Sears et. al., 2003). This finding was confirmed by the Tucson study, which demonstrated impaired lung function in infants even before their first LRI (Taussig, et. al., 2003).
7.3 AnSV\lers to the research and key questions
In order to determine whether children who spent their developing years in a polluted area in South Africa are unhealthy adults as far as their respiratory health status is concerned, it would be necessary to compare their respiratory health status to that of other adults who spent their developing years in a less polluted area in South Africa, preferably an area with similar climatic and socioeconomic conditions.
Due to capacity and cost constraints, such a cross-sectional study could not be performed and it was decided to compare the study population's respiratory health status to their own health status as children (which is known), the average for South Africa and to the average found in other studies conducted in less polluted areas.
The respiratory illnesses, hay fever and asthma, have increased significantly since childhood but on the other hand so did the prevalence of most allergic and autoimmune diseases worldwide. The prevalence of hay fever in 1990 (when the study population were children), did not differ from other surveys conducted during the same time on children in less polluted areas (Braun- Fahrlander, et. al., 1997; Martin, et. al.; 1997). The prevalence of asthma in the current study did not exceed the average for the South African white adult population. Hay fever and asthma are considered allergic diseases (Bach, 2002; Kramer, et. al. 1999) and studies found no associations with concentrations of PM, S02 and N02 (Braun-Fahrlander, et. al., 1997; Martin, et. al., 1997). In the current study, being allergic was the one statistically significant factor associated with all respiratory illnesses except pneumonia.
The prevalence of bronchitis (18%) in the current study was in the same order as the prevalence found in less polluted areas such as Switzerland (6-26%) and parts of the US (14%).
7.3.1 Answers to Key Questions
Is there a difference in the health status of adults who remained in the Vaal Triangle compared to those who left the area?
Univariate analysis found no statistically significant differences in any of the upper or lower respiratory health symptoms of individuals living in the Vaal Triangle compared with those who have left the area for more than two years already. For asthma, a higher risk (crude OR 2.7; p=0.103) for living outside the Vaal Triangle was observed. It is however possible that asthmatics have left the area.
Stepwise logistic regression revealed only one factor, namely that living outside
the Vaal Triangle was a marginally significant (p = 0.07) protection against sinusitis. Risk factors for suffering from sinusitis (being allergic and being overweight) were associated with genetic predisposition and life style.
Is there an association between health status and years spent in the polluted area?
Due to small numbers, the only way was to distinguish between the health status of those individuals who remained in the area and those who have left, as well as between those who have left but who visit the area for more than 30 days per year and those who do not No significant differences in upper or lower respiratory health symptoms could be observed between the aforementioned groupings. The risk for sinusitis was borderline.
Does the occupation of the individual play a role in his/her health status?
Working for more than a year in an environment exposed to chemicals and/or dust, increased the risk for pneumonia, asthma and hay fever in univariate analysis but not in stepwise logistic regression.
Does the risk of having upper respiratory illness increase significant with time spent in a polluted area during developing years?
As mentioned above, due to low numbers, the only groups ihatcould be studied, were those individuals who remained in the area and those who have left as well as those who have left but visiting the area for >30 days per year as opposed to those who have left but do not visit the area for 30 days or more per year. There was no significant difference in the prevalence of URI of those who remained in the Vaal Triangle (63%), (which include the 39% who were born there) and those who have left the area at some stage, as well as no significant difference in respiratory symptoms between those visiting the area for >30 days per year as opposed to those who do not.
Although numbers were small, asthma was used in an attempt to prove a difference between the groups. No significant difference (p=
0.~65)
wasobserved for the prevalence of asthma between those individuals who have always been living in the Vaal Triangle compared to those who had left the area between 4 and 10 years ago (results not shown).
Does the respiratory health status improve towards adulthood or does it stay the same (for those who remained in the area)?
The prevalence of most respiratory symptoms within the total study population has increasE?d since childhood with no statistical significant difference between those who remained in the area and those who have left.
What is the risk profile for respiratory diseases in adults who spent their developing years in a polluted area in South Africa?
The risk profile for respiratory diseases is graphically depicted in Figures 6.15 to 6.18. Having an allergy, was the one factor statistically significant associated with all respiratory symptoms except pneumonia. Risk factors related to lifestyle, such as smoking and being overweight formed part of the risk profile. According to the risk factors identified during univariate analysis, the individual with the highest risk would be an overweight allergic individual, who is either currently smoking or had been smoking at some stage, who is exposed to chemicals in the workplace and who has a perception that he or she lives in a polluted area.
CHAPTER EIGHT
8.0 Concllisions and Recommendations