We read with great interest the article by Mannes et al., which
related the adverse effects of ambient air pollution on birth weight.[1]
That article well described the effects of pollutant exposure on the risk
of low birth weight using a marker of small for gestational age (SGA).
However, that study presents some shortcomings.
First, gestational week at birth is obstetrically and sociall...
We read with great interest the article by Mannes et al., which
related the adverse effects of ambient air pollution on birth weight.[1]
That article well described the effects of pollutant exposure on the risk
of low birth weight using a marker of small for gestational age (SGA).
However, that study presents some shortcomings.
First, gestational week at birth is obstetrically and socially a more
important marker for infancy and childhood than birth weight.[2] In recent
studies such as Mannes�f, the gestational week at birth or both the
gestational week at birth and birth weight are used rather than birth
weight.[3] We are convinced that the gestational week should be
incorporated into their methods as an appropriate marker. Secondly, almost
all infants in multiple gestations are SGA even if the pregnancy course is
uneventful.[2] Accordingly, Mannes et al. were compelled to exclude
multiple gestations from the study materials. Finally, the blood-placental
barrier prevents various materials from passing through to the fetus in a
similar manner to that of the blood-brain barrier. Accordingly, it is
inferred that those materials do not easily reach the fetus even if they
can reach to the mother. Mannes et al.�fs study would have been better
researched and more useful if the above problems had been addressed in
their discussion section.
References
1) Mannes T, Jalaludin B, Morgan G et al. Impact of ambient air
pollution on birth weight in Sydney, Australia. Occup Environ Med
2005;62:524-30.
2) Cunningham FG, Leveno KJ, Bloom SL et al. Williams Obstetrics (22nd
edn) TX, McGraw-Hill 2005
3) Wiles NJ, Peters TJ, Leon DA et al. Birth weight and psychological
distress at age 45-51 years: results from the Aberdeen Children of the
1950s cohort study. Br J Psychiatry 2005;187:21-8.
We thank Dr. Rafnsson[1] for valuable comments on our paper.[2]
Rafnsson finds our policy implications surprising. In the light of present
evidence, we do not find further measures justified for reducing radiation
exposure among cabin crew. The justification for this view is the fact
that exposure limits common for all radiation workers, also apply for the
cabin crew. Dose monitoring indicates that the...
We thank Dr. Rafnsson[1] for valuable comments on our paper.[2]
Rafnsson finds our policy implications surprising. In the light of present
evidence, we do not find further measures justified for reducing radiation
exposure among cabin crew. The justification for this view is the fact
that exposure limits common for all radiation workers, also apply for the
cabin crew. Dose monitoring indicates that the cosmic radiation doses are
within the exposure limits. We see no reason to depart from the general
radiation protection principles.
Cohort studies have shown an excess risk of breast cancer in cabin
crew, in particular among those with long employment, with 1.5 – 3.4 fold
incidence compared with the general population.[e.g. 3] Nevertheless, the
radiation doses received are low and the expected effect based on previous
literature is very small, with RR well below 1.1.[4] Neither previous
studies nor our study have been able to identify the cause for the excess
incidence of breast cancer. Lack of association in our study does not
exclude the contribution of cosmic radiation in the development of breast
cancer, but it implies that other risk factors are likely to have a
greater role.
Rafnsson[1] finds our approach to occupational radiation dose
estimation crude. For cabin attendants, the only available source of
information on the number of flights during their career is the cabin
attendants themselves and thus, the questionnaire approach in exposure
assessment was appropriate. We used self-reported numbers of flights by
route and calendar period. We feel this is an improvement compared to
previous studies[e.g. 5-7], none of which have had any estimates of the
individual cosmic radiation dose. They have been based on surrogate
indicators such as length of employment or flight route type assignment.
Rafnsson[1] claims that we did not consider the possibility that
breast cancer can influence the subjects’ answers. Recall bias is
intrinsic in all case-control studies with subjects as source of
information and the issue was discussed in our paper.[2]
We excluded cabin attendants who worked for less than two years
because they had negligible exposure (due to very short period of cabin
work). In addition, several studies have shown that short-term employees
differ in terms of mortality and cancer risk from those with more stable
employment. Therefore, they are commonly excluded from occupational cohort
studies to avoid bias.
Our study has shortcomings inherent to retrospective case-control
study and to sparse data. Therefore, it cannot provide conclusive evidence
but does nevertheless supply new information. A large prospective follow-
up study with a large data set would be valuable. Currently, a
retrospective study, combining all the Nordic cabin crew cohorts with
comprehensive cancer incidence registration systems and improved dose
estimation algorithm is ongoing, and may be able to provide further
insight to the issue.
References
1. Rafnsson V. Retrospective assessment of exposure. Occup Environ
Med, electronic letter 25 Jul 2005.
2. Kojo K, Pukkala E, Auvinen A. Breast cancer risk among Finnish
cabin attendants: a nested case control study. Occup Environ Med
2005;62:488-493.
3. Pukkala E, Auvinen A, Wahlberg G. Incidence of cancer among
Finnish airline cabin attendants. BMJ 1995;311:649-652.
4. Boice JD Jr, Blettner M, Auvinen A. Epidemiologic studies of
pilots and aircrew. Health Phys 2000;79:576-684.
5. Haldorsen T, Reitan JB, Tveten U. Cancer incidence among Norwegian
airline cabin attendants. Int J Epidemiol 2001;30:825-830.
6. Rafnsson V, Sulem P, Tulinius H, et al. Breast cancer risk in
airline cabin attendants: a nested case-control study in Iceland. Occup
Environ Med 2003;60:807-809.
7. Reynolds P, Cone J, Layefsky M, et al. Cancer incidence in
California flight attendants (United States). Cancer Causes Control
2002;13:317-324.
In an interesting study published in the September 2005 issue of
Occupational and Environmental Medicine, Simoni and collegues reported the
relation between mould and/or dampness exposure and respiratory disorders
in children and adolescents in Italy [1]. The authors concluded that
wheeze and asthma can often be explained by exposure to home mould and
dampness, particularly in early life.
In an interesting study published in the September 2005 issue of
Occupational and Environmental Medicine, Simoni and collegues reported the
relation between mould and/or dampness exposure and respiratory disorders
in children and adolescents in Italy [1]. The authors concluded that
wheeze and asthma can often be explained by exposure to home mould and
dampness, particularly in early life.
Although the authors acknowledged the use of questionnaire data alone
to assess mould and dampness exposure will have limited their study, they
state that the validity of using questionnaires has been established.
In our own study, we investigated indoor exposure to dampness in 200
asthmatic and non-asthmatic children aged 4-17 [2]. We found that self-
reported dampness (by the parent/guardian) was significantly associated
with an asthmatic household, but no such association was found for
dampness observed by the field investigator or objective measures (using
an industrial dampmeter). Additionally, we have previously demonstrated
that the concordance between self-reported dampness and objective measures
is very poor [3]. In fact, there was almost complete disagreement between
self-reported dampness, visual inspection by a trained investigator and
measurement using an industrial dampmeter.
A study of the validity and determinants of reported home dampness
and moulds conducted by Dales et al reported evidence of systematic
reporting bias and recommended that objective measures rather than
questionnaires be used to clarify the health effects of indoor fungi [4].
Bearing in mind the evidence from these past studies, we feel that
the positive findings of Simoni et al should be interpreted with caution
and that all research involving home dampness should have some objective
data to back it up.
References
1) Simoni M, Lombardi E, Berti G et al. Mould/dampness exposure at
home is associated with respiratory disorders in Italian children and
adolescents: the SIDRIA-2 study. Occup Environ Med 2005; 62: 616-622.
2) Tavernier GO, Fletcher GD, Francis HC, Oldham LA, Fletcher AM,
Blacklock G, Stewart L, Gee I, Watson A, Frank TL, Frank P, Pickering CA,
Niven RM. Endotoxin exposure in asthmatic children and matched healthy
controls: results of IPEADAM study. Indoor Air. 2005;15 Suppl 10:25-32.
3) Frank TI, Pickering CAC, Fletcher G, Francis HC, Oldham LA, Kay
S, Frank P, Niven RMcL. (1999). Relationship between self reporting,
visible inspection and objective measurement of damp for determining damp
or mould contamination in houses. Proceedings of the 8th Internationional
Conference on Indoor Air Quality and Climate-Indoor Air '99, Vol. 2, pp564
-566.
4) Dales RE, Miller D and McMullen ED. Indoor air quality and
health: validity and determinants of reported home dampness and moulds.
International Journal of Epidemiology 1997; 26: 120-125.
Exposure period is as important as the dose of exposure
Based on Figure 1 in the article[1], it could be inferred that the
timing of dust exposure would be crucial when investigating whether “Dust
exposure” would increase the risk of IHD among patients who already had
Respiratory diseases: The dust exposure of most interest would be the
exposure after the occurrence of the respiratory dise...
Exposure period is as important as the dose of exposure
Based on Figure 1 in the article[1], it could be inferred that the
timing of dust exposure would be crucial when investigating whether “Dust
exposure” would increase the risk of IHD among patients who already had
Respiratory diseases: The dust exposure of most interest would be the
exposure after the occurrence of the respiratory diseases. However people
who were already diagnosed with respiratory disease especially those in
more serious conditions were more likely to be moved away from the
cohorts, therefore a great part of dust exposure among people with chronic
respiratory diseases were likely to happen before the diagnosis of the
respiratory diseases, may appear to have minimum direct effect on IHD.
Smoking: a rope
Moreover smoking as a great risk factor for both respiratory disease
and IHD, but this study only treat smoke habits as a categorical
variable[1], it is far from enough, for example only among subjects who
are current smokers, people who have higher dose of exposure on tobacco
smoke are more likely to have both respiratory disease as well as IHD.
However an analysis only include life long non-smokers may reduce the
shadow of bias in the picture. Furthermore it is unrealistic to measure
the effect of interaction between smoking and aspiratory disease on
incidence of IHD based on the assessments of exposures in this study.
Reference
1. Koskela R-S, M.p., Sorsa J-A, Klockars M, Respiratory disease and
cardiovascular morbidity. Occup. Environ, 2005. 62.
In their paper entitled “Risk of lymphatic or haematopoietic cancer
mortality with occupational exposure to animals or the public”, Svec et.
al.[1] clearly imply that they believe mortality is an acceptable
surrogate for incidence of haematological malignancy in this study group.
Although they offer certain caveats regarding this approach, they ignore
the greatest potential confounder. Patients with...
In their paper entitled “Risk of lymphatic or haematopoietic cancer
mortality with occupational exposure to animals or the public”, Svec et.
al.[1] clearly imply that they believe mortality is an acceptable
surrogate for incidence of haematological malignancy in this study group.
Although they offer certain caveats regarding this approach, they ignore
the greatest potential confounder. Patients with haematological
malignancies are, by virtue of their disease, therapy or both, very likely
to be immunocompromised, often severely. As a consequence of this
immunoparesis, these patients may be expected to be much more vulnerable
to zoonotic infections and patients with occupational contact with animals
will be much more frequently exposed to such infections than patients with
other occupations.
To validate the use of mortality as a surrogate for incidence in this
cohort, it is necessary to rule out differential mortality from infection
between cases and controls affected by haematological malignancy. There is
no evidence in this paper that Svec et. al. have considered this potential
confounding factor. Absent such consideration, it is not possible to draw
any causal inference between occupations involving animal exposure and the
risk of developing a lympho-haemopoeitic malignancy as opposed to the risk
of dying from such a condition. A further analysis would be required
considering the proximate cause of death, rather than just the underlying
cause.
Yours sincerely,
Kenneth Campbell MSc (Clinical Oncology)
Reference List
1. Svec MA, Ward MH, Dosemeci M, Checkaway H, De Roos AJ. Risk of
lymphatic or haematopoietic cancer mortality with occupational exposure to
animals or the public. Occup Environ Med 2005;62:726-35.
Dear Editor,
We read with great interest the article by Mannes et al., which related the adverse effects of ambient air pollution on birth weight.[1] That article well described the effects of pollutant exposure on the risk of low birth weight using a marker of small for gestational age (SGA). However, that study presents some shortcomings.
First, gestational week at birth is obstetrically and sociall...
Dear Editor,
We thank Dr. Rafnsson[1] for valuable comments on our paper.[2] Rafnsson finds our policy implications surprising. In the light of present evidence, we do not find further measures justified for reducing radiation exposure among cabin crew. The justification for this view is the fact that exposure limits common for all radiation workers, also apply for the cabin crew. Dose monitoring indicates that the...
Dear Editor
In an interesting study published in the September 2005 issue of Occupational and Environmental Medicine, Simoni and collegues reported the relation between mould and/or dampness exposure and respiratory disorders in children and adolescents in Italy [1]. The authors concluded that wheeze and asthma can often be explained by exposure to home mould and dampness, particularly in early life.
...Dear Editor
Exposure period is as important as the dose of exposure
Based on Figure 1 in the article[1], it could be inferred that the timing of dust exposure would be crucial when investigating whether “Dust exposure” would increase the risk of IHD among patients who already had Respiratory diseases: The dust exposure of most interest would be the exposure after the occurrence of the respiratory dise...
Dear Editor,
In their paper entitled “Risk of lymphatic or haematopoietic cancer mortality with occupational exposure to animals or the public”, Svec et. al.[1] clearly imply that they believe mortality is an acceptable surrogate for incidence of haematological malignancy in this study group. Although they offer certain caveats regarding this approach, they ignore the greatest potential confounder. Patients with...
Pages