Bless et al. BMC Res Notes (2017) 10:266
DOI 10.1186/s13104-017-2587-8
RESEARCH NOTE
The recurrent campylobacteriosis
epidemic over Christmas and New Year
in European countries, 2006–2014
Philipp Justus Bless1,2
, Claudia Schmutz1,2
  and Daniel Mäusezahl1,2*
 
Abstract 
Objective:  Campylobacteriosis is the most frequently reported foodborne disease in Europe with a notification rate
of 71 per 100,000 population in the European Union in 2014. Surveillance data show a clear seasonality whereby
case numbers peak during summer months in entire Europe and at the turn of the year, especially in Germany and
Switzerland. A detailed description of European surveillance data by country at the turn of the year was missing so far.
The objectives of the presented work were to describe national surveillance data of The European Surveillance System
for 14 countries during winter times and to generate hypotheses for the observed seasonality of campylobacteriosis
cases.
Results:  The analysis included 317,986 cases notified between calendar weeks 45 and 8 of winter seasons
2006/2007–2013/2014. Winter peaks in weekly case notifications and notification rates were observed for Austria, Belgium,
Finland, Germany, Luxembourg, The Netherlands, Switzerland and Sweden while for Denmark, France, Ireland,
Italy, Norway and the United Kingdom no unusual increase was observed. Generally, weekly notification rates peaked
in calendar week 1 or 2 after a strong decline in the last week of December and reached values of a multiple of the
observed notification rates in the weeks before or after the peak e.g. up to 6.5 notifications per 100,000 population
per week in Luxembourg. Disease onset of cases notified during winter peaks occurred predominantly in calendar
weeks 52 and 1 and point towards risk exposures around Christmas and New Year. The consumption of meat fondue
or table top grilling poses such a risk and is popular in many countries with an observed winter peak. Additionally,
increased travel activities over the festive season could foster campylobacteriosis transmission. Surveillance artefacts
(e.g. reporting delays due to public holidays) should be excluded as causes for country-specific winter peaks before
investigating risk exposures.
Keywords:  Campylobacter, Infectious disease surveillance, Europe, Seasonality,
The European Surveillance System (TESSy)
© The Author(s) 2017. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License
(http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium,
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Introduction
Since 2005, human campylobacteriosis has been the
most frequently reported foodborne bacterial gastrointestinal
disease in Europe. Case numbers are increasing
[1]. In 2014, around 237,000 cases were reported by
26 European Union (EU) member states corresponding
to a notification rate of 71 per 100,000 population [1].
European campylobacteriosis surveillance data show
a clear seasonal trend [2]. The number of notified cases
starts to increase drastically in April and peaks during
summer, between June and August [2]. The lowest numbers
of cases are notified in February and March [2]. In
the campylobacteriosis surveillance data of the EU, in
particular of Germany, and of Switzerland, an additional
seasonal peak between late December and early January,
the so-called winter peak, has been described [1, 3, 4].
The monthly incidence in Germany peaks in January [3]
and case numbers in Switzerland increase during the last
week of December and the 1st week of January [4].
Open Access
BMC Research Notes
*Correspondence: daniel.maeusezahl@unibas.ch
1
Swiss Tropical and Public Health Institute, Socinstrasse 57, P. O. Box 4002,
Basel, Switzerland
Full list of author information is available at the end of the article
Page 2 of 7Bless et al. BMC Res Notes (2017) 10:266
Our investigation of the winter peak in Switzerland
identified the consumption of meat fondue as main risk
factor, especially if served with chicken [5]. Meat fondue
is traditionally consumed on Christmas day and
on New Year’s Eve in Switzerland and is also a popular
dish at New Year’s Eve in Germany and Luxembourg [5,
6]. A detailed description of European Campylobacter
surveillance data at the turn of the year is missing so far
and hence, it is unknown in which other European countries
winter peaks in notification data occur. This study
analyses European country-specific surveillance data at
the turn of the year from 2006 to 2014, to determine if
winter peaks as observed in Switzerland and Germany
also occur in other European countries and to generate
hypotheses for the seasonal patterns.
Main text
Analysis of Campylobacter surveillance data
This study considered Switzerland, Germany and neighbouring
countries (Austria, Belgium, France, Italy, Luxembourg,
The Netherlands), countries of the British Isles
(Ireland, United Kingdom) and Nordic countries (Denmark,
Finland, Norway, Sweden). For EU member states,
case-based notification data on laboratory-confirmed
Campylobacter infections from 2006 to 2014 originated
from The European Surveillance System (TESSy)—an
indicator-based surveillance database for communicable
diseases hosted by the European Centre for Disease
Prevention and Control (ECDC) [7]. Surveillance data
from the National Notification System for Infectious Diseases
on laboratory-confirmed campylobacteriosis cases
notified between 2006 and 2014 were used for Switzerland.
Our previous analysis of Swiss notification data on
Campylobacter showed that the winter peak is rather a
short-term phenomenon and better observable in weekly
than monthly notification data [4]. Therefore, we performed
a descriptive analysis of country-specific weekly
notification data focusing on the period of calendar
weeks 45 to 8.
A total of 1,530,564 campylobacteriosis case notifications
were received from TESSy. For 147 case notifications
or 0.03% of all United Kingdom notifications no
information on the week of notification was available.
Hence, they were excluded from further analyses. In 2006
and 2007 German notification data were reported on
a monthly basis leading to the exclusion of 118,142 case
notifications. We additionally excluded 848 case notifications
with a notification date in 2006 or 2014 but
belonging to calendar week 52 of 2005 or calendar week
1 of 2015. For Italy no notification data from 2006 until
mid-2008 were available. A total of 317,986 cases notified
between calendar weeks 45 and 8 of the winter seasons
2006/2007–2013/2014 were analysed including 16,237
campylobacteriosis cases from Switzerland.
Weekly notification rates were calculated using annual
country-specific population numbers as per 1st of January
for each corresponding winter season from the
Eurostat database [8]. The Dutch and French sentinel
surveillance systems do not cover the whole population.
We used the estimated population coverage for Campylobacter
surveillance of 52% (The Netherlands) and 20%
(France) [2] to calculate population numbers for the calculation
of weekly notification rates. The population coverage
of Campylobacter sentinel surveillance in Belgium
and Italy is unknown and, hence, only case numbers were
used. The sum of case numbers and the median of notification
rates over all winter seasons are presented for
each calendar week by country. Additionally, dates of disease
onset or diagnosis were analysed to assess possible
reporting delays. In the Additional file  1 case numbers
and notification rates per calendar week for each winter
season and country are presented.
Seasonal patterns of campylobacteriosis
The sum of case notifications and the median of notification
rates by calendar week over all years increased at
the end of December or beginning of January for Austria,
Belgium (case notifications only), Finland, Germany,
Luxembourg, The Netherlands, Sweden and Switzerland
and decreased towards the end of January (Fig. 1). Winter
peaks in terms of median notification rates were most
pronounced in Luxembourg and Switzerland with peak
rates of 2.9 and at 3.2 per 100,000 population, respectively
(Table  1). Less pronounced winter peaks were
observed in The Netherlands and Austria with peak rates
of 1.1 and 1.3 per 100,000 population, respectively. The
sum of weekly case notifications in Belgium peaked in
week 2. For the other countries (Denmark, France, Ireland,
Italy, Norway and the United Kingdom) no unusual
increase during the winter season was observed (Fig. 1).
A common characteristic of most countries was that the
sum of case numbers and median notification rates were
lowest at the end of December in week 52.
The weekly case numbers and notification rates of
winter peaks varied in each country by year (Additional
file 1). The most distinct winter peak with a weekly notification
rate of 6.5 per 100,000 population was observed
in Luxembourg during the winter season 2013/2014
(Table 2). Peak rates in other countries ranged from 1.8
in Germany and The Netherlands to 4.5 notifications
per 100,000 population in Switzerland. From the beginning
of the observation period in 2006/2007–2013/2014
peak case numbers and notification rates increased for
Belgium, Germany, Luxembourg, The Netherlands, Sweden
and Switzerland (Table  2). A more than threefold
Page 3 of 7Bless et al. BMC Res Notes (2017) 10:266
Fig. 1  Number of case notifications and weekly notification rates per 100,000 population for campylobacteriosis in selected European countries,
winter seasons 2006/2007–2013/2014. a
Sum of weekly notifications from winter seasons 2006/2007–2013/2014 (Germany and Italy: 2008/2009–
2013/2014). b
Weekly notifications per 100,000 population = median of weekly notification rates from winter seasons 2006/2007–2013/2014 (Germany
2008/2009–2013/2014). c
Sum of weekly notifications only as coverage of surveillance system unknown. Note: Scales of y-axes differ between
countries
Page 4 of 7Bless et al. BMC Res Notes (2017) 10:266
increase was observed for Luxembourg and a twofold
increase for Switzerland. For Austria and The Netherlands
winter peaks in 2006/2007 had higher peak rates
compared to the subsequent years but afterwards peak
rates started to increase discontinuously. In Austria peak
rates increased by 45% from 1.1 to 1.6 notifications per
100,000 population between 2011 and 2014. The highest
rate of the winter peak 2007/2008 in The Netherlands
was 0.7 per 100,000 population and increased to twice
this rate in 2013/2014.
The Nordic countries Denmark and Norway exhibited
no specific dynamics in the annual notification data on a
regular basis (Additional file 1). However, Danish weekly
case numbers and notification rates showed irregular
increases resembling a winter peak during some winter
seasons. In Norway case numbers and notification rates
generally decreased around calendar weeks 51 and 52
and were sometimes slightly increased in calendar weeks
1, 2, or 3.
Possible reporting delays were assessed for countries
with observable winter peaks and for which dates of disease
onset or dates of diagnosis were available (Austria,
Belgium, Germany and Norway). Numbers of disease
onset or diagnosis were summed up over all years per day
and are depicted in Fig. 2. In Austria, Germany and Norway
the daily numbers of disease onset peaked in the first
week of January and to a smaller extent already in the last
week of December. Peaks of disease onset dates occurred
a few days to 1  week before winter peaks observed in
actual notification data. The number of diagnoses in
Belgium started to increase at the end of December and
decreased after the 2nd week of January.
Our analysis of notification data shows that seasonal
transmission of Campylobacter infection occurs prominently
and distinctively during winter time in many European
countries. Weekly notification rates can increase
up to a multiple of the observed notification rates in the
weeks before or after the winter peaks. In Switzerland
Table 1  Winter peaks of campylobacteriosis case notifications as median notification rate and sum of case notifications
over all winter seasons, 2006/2007–2013/2014
N/A not applicable
a
  Rate per 100,000 population
Country Calendar week of peak Median notification ­ratea
Sum of case notifications
Austria 2 1.3 887
Belgium 2 N/A 1302
Finland 2 1.7 719
Germany 2 1.5 8807
Luxembourg 2 2.9 116
The Netherlands 1 1.1 733
Sweden 3 1.6 1250
Switzerland 1 3.2 1964
Table 2 Weekly peak notification rates over  winter seasons and  changes of  weekly peak notification rates
between 2006/2007 and 2013/2014 winter seasons
a
  Rate per 100,000 population
b
  Winter peak 2008/2009
Country Maximum weekly notification rate
of all winter peaks
Maximum weekly notification
rate of winter peak 2006/2007
Maximum weekly notification
rate of winter peak 2013/2014
Change
of maximum
weekly notification
rates
(2006/2007–
2013/2014) (%)
Notification
­ratea
Calendar week Year Notification
rate
Calendar week Notification
rate
Calendar week
Austria 1.9 2 2007 1.9 2 1.6 3 −15.8
Finland 3.1 50 2007 1.4 3 1.7 3 +21.4
Germany 1.8 2 2014 1.7b
3b
1.8 2 +5.9
Luxembourg 6.5 3 2014 1.9 2 6.5 3 +242.1
The Netherlands 1.8 1 2012 1.2 2 1.4 2 +16.7
Sweden 2.0 3 2008 1.5 3 1.5 3 0.0
Switzerland 4.5 1 2012 1.7 2 3.6 1 +111.8
Page 5 of 7Bless et al. BMC Res Notes (2017) 10:266
and The Netherlands the notification rates already
peaked in the 1st week of January whereas rates for the
remaining countries peaked rather in week 2. So far this
short-term phenomenon was described in the literature
for Germany [3], Switzerland [4, 5] and Luxembourg [6].
For the EU the observation of a winter peak in January
was reported for the first time for the years 2012–2014
[1].
Median notification rates over all winter seasons generally
increase suddenly in the 1st week of January after
a strong decline in the last week of December and do
peak in January. The strong decline at the end of December,
also observable in countries without a winter peak,
could be due to limited access to health care services
and reporting delays during public holidays at the end
of the year. A study on campylobacteriosis notification
data of England and Wales showed that the reporting
rate is lower during weeks with a public holiday sometimes
resulting in additional reporting in the following
week [9]. Annual weekly notification rates of winter
peaks showed an increasing trend over the recent years
in most affected countries which could be related to the
general increase of campylobacteriosis case notifications
in Europe since 2005 [1, 2]. The analysis of Austrian, Belgian,
German and Norwegian dates of disease onset and
of diagnosis revealed that most notified cases show symptoms
of campylobacteriosis in the last week of December
and the 1st  week of January. This observation was
recently described for Germany [3]. Hence, winter peaks
seen in surveillance data are likely delayed by a few days
to 1  week compared to actual peaks of campylobacteriosis
in the population when considering the “date used
for statistics” of TESSy. These delays are likely caused by
time needed for health care seeking, laboratory diagnostics
and reporting. When taking into account an average
incubation period for campylobacteriosis of 2–5  days,
exposure to Campylobacter occurs likely around Christmas
or New Year for notifications reported in the first
2 weeks of January [3, 5].
Possible reasons for the seasonal patterns
The sudden increases of weekly notification rates point
towards a rapid change in exposure patterns or levels of
exposures for campylobacteriosis in winter. Of particular
interest appear food- and travel-related exposures
around Christmas and New Year. In Finland and Sweden
high proportions of travel-related cases (≥50%) are
observed in annual surveillance data [1, 2]. Their winter
peaks may be partially due to increased travel activities
to foreign countries during Christmas and New Year
Fig. 2  Sum of case notifications between 1st December and 31st January. a Austria by daily disease onset, winter seasons 2008/2009–2013/2014. b
Germany by daily disease onset, winter seasons 2008/2009–2013/2014. c Norway by daily disease onset, winter seasons 2006/2007–2013/2014.
d Belgium by daily diagnoses, winter seasons 2011/2012–2012/2013
Page 6 of 7Bless et al. BMC Res Notes (2017) 10:266
holidays. In Switzerland, travelling abroad during the festive
season was associated with almost three-time higher
odds for contracting campylobacteriosis [5].
A recent study in Luxembourg identified the consumption
of chicken in winter as risk factor for contracting
campylobacteriosis and the authors hypothesised that it
could be related to the traditional consumption of meat
fondue during this time [6]. The consumption of meat
fondue or table top grilling during the festive season is
popular in Austria, Belgium, Germany, Luxembourg and
The Netherlands. In Switzerland, the campylobacteriosis
winter peak is associated with the frequent consumption
of meat fondue at Christmas and New Year which
increased the odds for contracting campylobacteriosis
fourfold [5]. At these occasions, possibilities for Campylobacter
transmission include cross-contamination of
cooked meat and/or side dishes by raw poultry meat and
individual meat preparation at the table [5, 10]. Hence,
individuals are likely to contract campylobacteriosis
around Christmas and New Year as a consequence of
increased exposure levels to foodborne and travel-related
risk factors.
Limitations
The “date used for statistics” provided by TESSy can vary
between reporting countries and could mean the dates of
disease onset, of diagnosis, of notification or any other
date. The use of a non-standardised reporting date and
differences in the national surveillance systems make it
difficult to exactly compare the temporal trends of winter
peaks among countries. Reporting delays and other surveillance
artefacts affecting notification rates of observed
winter peaks could not be excluded. Consequently, it
should be evaluated whether these peaks represent a true
epidemiological trend before investigating possible risk
exposures. To our knowledge, there is no scientific evidence
on the extent and significance of the consumption
of meat fondue or table top grilling for the investigated
countries except for Switzerland [5].
Abbreviations
ECDC: European Centre for Disease Prevention and Control; EU: European
Union; TESSy: The European Surveillance System.
Authors’contributions
All authors made substantial contributions to the conception and design of
the study, data analysis and interpretation of results. PJB wrote the first draft of
the manuscript and all authors critically revised the manuscript for important
intellectual content. All authors read and approved the final manuscript.
Additional file
Additional file 1. Country-specific case numbers and notification rates
for winter seasons 2006/2007–2013/2014.
Author details
1
 Swiss Tropical and Public Health Institute, Socinstrasse 57, P. O. Box 4002,
Basel, Switzerland. 2
 University of Basel, Petersplatz 1, P. O. Box 4001, Basel,
Switzerland.
Acknowledgements
The authors gratefully acknowledge access to data from The European Surveillance
System—TESSy, provided by Austria, Belgium, Germany, Denmark,
Finland, France, Ireland, Italy, Luxembourg, The Netherlands, Norway, Sweden
and The United Kingdom and released by ECDC. The surveillance data for
Switzerland were kindly provided by the Federal Office of Public Health, Bern,
Switzerland. We thank Thomas A. Smith (Swiss Tropical and Public Health
Institute, Basel, Switzerland) for the critical review of the manuscript.
Competing interests
The authors declare that they have no competing interests.
Availability of data and materials
The data that support the findings of this study are available from TESSy,
ECDC, Stockholm, Sweden and the Swiss Federal Office of Public Health, Bern,
Switzerland but restrictions apply to the availability of these data, which were
used under license for the current study, and so are not publicly available.
Disclaimer
The views and opinions of the authors expressed herein do not necessarily
state or reflect those of ECDC. The accuracy of the authors’statistical analysis
and the findings they report are not the responsibility of ECDC. ECDC is not
responsible for conclusions or opinions drawn from the data provided. ECDC
is not responsible for the correctness of the data and for data management,
data merging and data collation after provision of the data. ECDC shall not be
held liable for improper or incorrect use of the data.
Ethics approval and consent to participate
Access to routine surveillance data was granted by TESSy, ECDC, Stockholm,
Sweden and the Federal Office of Public Health, Bern, Switzerland according
to the institutions’data sharing policies following formal requests of the
authors. The case-based data sets received by the authors contained no
personal identifiers.
Funding
The financial support of the Ph.D. Program Health Sciences (PPHS) of the
University of Basel and the Rudolf Geigy Foundation, Basel, Switzerland to conduct
the work is appreciated. The funders did not play any role in the design
of the study and collection, analysis and interpretation of data, and in writing
the manuscript.
Publisher’s Note
Springer Nature remains neutral with regard to jurisdictional claims in published
maps and institutional affiliations.
Received: 11 March 2017 Accepted: 29 June 2017
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