Dethlefsen, Claus

Lundbye-Christensen, Søren

Schønheyder, Henrik

Thomsen, Reimar W.

Tvedebrink, Torben

The seasonal nature of invasive pneumococcal disease with peak incidences during winter months is well recognized (Dowell 2003, Talbot 2005, Watson 2006). However few detailed studies of the temporal relationship between actual climatic changes and subsequent pneumococcal disease are available. We perform an 8-year longitudinal population-based ecological study in a Danish county to examine whether foregoing changes in meteorological parameters, including temperature, relative humidity, precipitation, and wind velocity, predicted variations in pneumococcal bacteremia (PB) incidence.The seasonal nature of invasive pneumococcal disease with peak incidences during winter months is well recognized (Dowell 2003, Talbot 2005, Watson 2006). However few detailed studies of the temporal relationship between actual climatic changes and subsequent pneumococcal disease are available. We perform an 8-year longitudinal population-based ecological study in a Danish county to examine whether foregoing changes in meteorological parameters, including temperature, relative humidity, precipitation, and wind velocity, predicted variations in pneumococcal bacteremia (PB) incidence

    Aalborg UniversitetMeteorological effects on the incidence of pneumococcal bacteremia in DenmarkTvedebrink, Torben; Lundbye-Christensen, Søren; Thomsen, Reimar W.; Dethlefsen, Claus;Schønheyder, HenrikPublication date:2007Document VersionPublisher's PDF, also known as Version of recordLink to publication from Aalborg UniversityCitation for published version (APA):Tvedebrink, T., Lundbye-Christensen, S., Thomsen, R. W., Dethlefsen, C., & Schønheyder, H. (2007).Meteorological effects on the incidence of pneumococcal bacteremia in Denmark. Poster session presented atForskningens Dag, Aalborg, Denmark.General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright ownersand it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.            ? Users may download and print one copy of any publication from the public portal for the purpose of private study or research.            ? You may not further distribute the material or use it for any profit-making activity or commercial gain            ? You may freely distribute the URL identifying the publication in the public portal ?Take down policyIf you believe that this document breaches copyright please contact us at vbn@aub.aau.dk providing details, and we will remove access tothe work immediately and investigate your claim.Downloaded from vbn.aau.dk on: April 30, 2017Meteorological eﬀects on the incidenceof pneumococcal bacteremia in DenmarkTorben Tvedebrinka, Søren Lundbye-Christensena,b,Reimar W. Thomsenc, Claus Dethlefsend, Henrik C. SchønheydereaDepartment of Mathematical Sciences, Aalborg University; bDepartment of Health Science and Technology, Aalborg University;cDepartment of Clinical Epidemiology, Aalborg Hospital, Aarhus University Hospital; dCenter for Cardiovascular Research, Aalborg Hospital,Aarhus University Hospital; eDepartment of Clinical Microbiology, Aalborg Hospital, Aarhus University Hospital.IntroductionThe seasonal nature of invasive pneumococ-cal disease with peak incidences during win-ter months is well recognized (Dowell 2003,Talbot 2005, Watson 2006). However few de-tailed studies of the temporal relationship be-tween actual climatic changes and subsequentpneumococcal disease are available. We per-form an 8-year longitudinal population-basedecological study in a Danish county to exam-ine whether foregoing changes in meteorologi-cal parameters, including temperature, relativehumidity, precipitation, and wind velocity, pre-dicted variations in pneumococcal bacteremia(PB) incidence.YearPneumonia incidence1995 1996 1997 1998 1999 2000 2001 2002 2003014916Temperature [C°]20151050−5Pneumonia incidence TemperatureFig. 1. The observed points with fitted sinusoids superimposed. Temperature is on reversed scale.MethodsWe included cases of PB that occurred fromJanuary 1995 through December 2002 in NorthJutland County, Denmark, with a populationof 492,845 individuals on average during the pe-riod of study. Patients with PB were deﬁned asindividuals with a clinical disease episode withStreptococcus pneumoniae detected by bloodculture.Meteorological data were available in terms ofdaily summaries from a weather station corre-sponding to the area under study. Daily meanvalues were calculated for temperature (mini-mum, mean and maximum), relative humidity,precipitation and wind velocity.We ﬁtted a harmonic sinusoidal regressionmodel to estimate the exact phase diﬀerence indays between changes in each of the meteoro-logical variables and PB incidence. The modelwas given by A cos(2(t−φ)/365.25)+B whereφ is the phase that indicates the location of theseasonal peak. Since the PB incidence countswere assumed Poisson distributed we took asquare root transformation. The diﬀerences indays between the phase of PB incidence andeach of the meteorological variables were de-termined together with a 95% conﬁdence inter-val (CI). The sign and magnitude of the phasediﬀerence indicated whether the meteorologicalvariable aﬀected the intensity of pneumonia.ResultsDuring the eight years of surveillance, 63,166blood cultures were performed and 714episodes of PB were detected. We observed2,329 days with no PB episodes and 493, 82, 15,3 days with one, two, three and four episodesrespectively, giving 2,922 days in the time span.The estimated phase diﬀerences between PBincidence and the diﬀerent meteorological vari-ables are given in Table 1.Phase diﬀerence in daysTemperature -16 (-18 ; -14)Minimum temperature -13 (-15 ; -11)Maximum temperature -19 (-22 ; -17)Wind velocity 3 (1 ; 5)Relative humidity -59 (-65 ; -52)Precipitation 28 (2 ; 55)Table 1: Phase diﬀerences for pneumonia andthe meteorological variables in days with 95%-CI in brackets.The only negative diﬀerences were found fortemperature (minimum, mean and maximum)and relative humidity, indicating that thesevariables were shifted to the left relative to PBand in particular attained their minimum andmaximum, respectively, earlier than the PB in-cidence was at its maximum. A close inverserelationship was found between temperaturechanges and PB incidence, with an observedtime lag of 16 (95% CI, 14-18) days betweentemperature peaks and troughs and PB activ-ity. Peaks in relative humidity preceded PBpeaks by about 2 months. These relationshipswere seen independently of a strong seasonalpattern of PB. No relationship was found be-tween PB incidence and precipitation or windvelocity.Figure 1 shows monthly PB incidences togetherwith the monthly mean temperatures duringthe 8-year study period. Superimposed arethe ﬁtted sinusoids showing the lag of approxi-mately two weeks between pneumonia and tem-perature. Graphical inspection of the resid-uals indicated that observed PB incidenceshigher than predicted by the model were seenin months with lower than modeled tempera-tures.DiscussionOur analyses conﬁrmed a distinctive seasonalvariation in the incidence of PB in Denmarkwith similar summer troughs and winter peaksas have been reported from several states inthe US and from a temperate region in Aus-tralia (Dowell, Watson, Talbot). Our ﬁndingsare in line with one previous study from Aus-tralia that examined the relationship betweenPB and similar speciﬁc climatic parameters asin our study, ﬁnding a strong inverse relation-ship between weekly mean maximum and min-imum temperature and PB activity in the pop-ulation, whereas other examined climatic pa-rameters were unrelated to PB (Watson).We speculate, that the approximately 2 weeksbetween temperature drops and PB peaks mayrepresent the time lag from increased indoorcrowding due to cold weather, increased trans-mission of respiratory viruses together with ex-change of new pneumococcal serotypes amongchildren, transmission to adult contacts ofboth, increased occurrence of viral upper respi-ratory tract infection, followed by pneumococ-cal pneumonia and admission with PB.ConclusionWe found that changes in temperature closelypredicted pneumococcal bacteremia incidencepeaks, independently of seasonal patterns.

Meteorological effects on the incidence of pneumococcal bacteremia in Denmark

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Meteorological effects on the incidence of pneumococcal bacteremia in Denmark

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