The Influence of Climate on Invasive Haemophilus
Disease and Respiratory Infections in Children
Jodie McVernon*, Mark A Saunders , Paul Rockett , E Richard Moxon*
*Oxford Vaccine Group, University of Oxford Department of Paediatrics, John Radcliffe
Hospital
Benfield Greig Hazard Research Centre, Department of Space and Climate Physics, University
College London
Short Report — 599 words
Submitted to the British Medical Journal
March 2002
Corresponding author:
Dr Jodie McVernon, Oxford Vaccine Group, Department of Paediatrics, John Radcliffe
Hospital, Headley Way, Headington, Oxford, OX3 9DU, United Kingdom
Telephone/facsimile: +44 1865 221068
E-mail: jodie.mcvernon@paediatrics.ox.ac.uk
Introduction
A recent increase in the incidence of Haemophilus influenzae type b (Hib) vaccine failures in
children under 5 years of age in the UK has been noted, from 0.35 per 105 in 1998 to 2.65 in
2001. In considering factors involved in the pathogenesis of infection, we studied the influence
of interannual seasonal to monthly climate variability over the years 1993-2000 on the incidence
of (i) invasive disease due to Hib and capsule deficient or non typable Haemophilus influenzae
(NT Hi) and (ii) common cold and otitis media, illnesses which may potentially contribute to
invasive bacterial infection.
Participants, methods and results
Four weekly and seasonal incidence rates of invasive disease due to Hib and NT Hi in vaccinated
children under 5 in England and Wales were calculated. 204 cases of Hib and 162 cases of NT
Hi were reported to the Public Health Laboratory Service (PHLS), Oxford Vaccine Group and
British Paediatric Surveillance Unit between October 1992 and October 20011. Denominators
were based on England and Wales livebirths (Office of National Statistics) and PHLS data on
Hib vaccination coverage. The incidence of common cold and otitis media was obtained from the
Weekly Returns Service of the Royal College of General Practitioners, who receive reports of
new diagnoses of illness based on clinical impression from 72 sentinel practices in England and
Wales2.
The association between disease incidence and Central England mean Temperature and
England and Wales Rainfall was examined using linear regression analyses on pooled 4 weekly
data.
Variation in the mean and standard deviation of the common cold and otitis media
datasets, possibly due to changes in reporting methods over time, were controlled for using a
linear detrend. Relationships between disease and climate were examined across years within
each season and each 4 weekly time period.
Results are shown in Table 1. There was no significant correlation between Hib and
climate. However, significant negative associations with temperature were seen for NT Hi,
common cold and otitis media. This link was most marked in autumn, particularly weeks 41-44
(October). No consistent relationship with precipitation was seen.
Comment
No significant association was found between climate and invasive Hib disease incidence in
children. In contrast, a significant negative relationship was observed between year-on-year
temperature variation and the incidence of NT Hi, common cold and otitis media. Similar
negative temperature links have been reported in studies of pneumococcal disease3,4.
The association of lower temperatures with invasive bacterial infection has been attributed
to an increase in viral respiratory infections and otitis media in autumn and winter, which may
lower host defences3. The link may also arise from additional time spent indoors in colder
temperatures enhancing the opportunity for transmission of organisms4.
Whatever the
mechanism, climate effects on health appear more marked where the ability to modify indoor
temperature is less. Lower temperature is associated with an increase in upper and lower
respiratory tract infections in children in Lahore, Pakistan, with those living in poor quality
slum housing at greatest risk4. Excess winter mortality in elderly people in the UK is highest in
fuel poor households, unable to adequately heat their thermally inefficient homes5.
The lack of association between Hib and temperature is surprising, and may reflect either
Hib s increased virulence, or a change in the epidemiology of disease attributable to vaccination.
Other datasets collected preferably over a longer time period would be needed to confirm this
finding. However, ecological studies are unable to describe effects occurring in individual cases.
We believe the contribution of temperature and housing requires exploring as part of a case
control study of socio-economic factors associated with invasive Haemophilus influenzae and
respiratory diseases in children.
Acknowledgements
We wish to thank Dr Douglas Fleming, Director of the Birmingham Research Unit of the
Royal College of General Practitioners, for his collaboration in providing the Weekly Returns
Service data.
References
1. McVernon J. Invasive Haemophilus influenzae infection. In: British Paediatric Surveillance
Unit 15th Annual Report 2000-2001. Royal College of Paediatrics and Child Health, London
2001.
2. Fleming DM. Weekly returns service of the Royal College of General Practitioners. Comm
Dis Pub Health 1999; 2:96-100.
3. Kim PE, Musher DM, Glezen P, Rodriguez-Barradas MC, Nahm WK, Wright CE.
Association of invasive pneumococcal disease with season, atmospheric conditions, air
pollution, and the isolation of respiratory viruses. Clin Infect Dis 1996; 22:100-6.
4. Erling V, Jalil F, Hanson LA, Zaman S. The impact of climate on the prevalence of
respiratory tract infections in early childhood in Lahore, Pakistan. J Public Health Med
1999; 21(3):331-9.
5. Wilkinson P, Landon M, Armstrong B, Stevenson S, Pattenden S, Mckee M, Fletcher T.
Cold Comfort.
The social and environmental determinants of excess winter death in
England, 1986-96. The Policy Press, Bristol UK 2001.
Table 1. Relation between the interannual variability in Central England Temperature and disease
incidence for weeks 41-44 (October) 1993-2000
Haemophilus
Influenzae
Type b
Non Capsulate
Haemophilus
Influenzae
Common Cold
Otitis Media
Raw
Detrended
Raw
Detrended
Raw
Detrended
Raw
Detrended
Slope Coefficient
0.006
0.007
-0.022
-0.018
-116
-92.4
-52.7
-38.4
Standard Error
0.013
0.013
0.010
0.005
65.2
29.2
38.2
13.5
p-value
0.65
0.63
0.08
0.02
0.13
0.02
0.22
0.03
Intercept
0.045
0.000
0.267
0.000
2389
0.00
1038
0.00
0.136
0.018
0.103
0.007
668
39.5
392
18.3
0.04
0.04
0.43
0.65
0.34
0.62
0.24
0.57
Standard Error
R-Square
The Central England Temperature and disease time series are linearly detrended prior to computing the detrended results. The slope
coefficient and intercept units are 4-weekly incidence per 105 children for Haemophilus Influenzae Type b and Non Capsulate
Haemophilus Influenzae, and weekly incidence per 105 children for Common Cold and Otitis Media.