| Objectives
EARSS is an international network of national surveillance systems,
which aims to aggregate comparable and reliable antimicrobial resistance data to benefit
public health across Europe. Taking into account laboratory methods as well as
epidemiological principles, EARSS will explore the feasibility of analysing regional
differences, assessing risk factors, and providing electronic feedback in a study of 18
months duration. Microbiologists and epidemiologists from participating countries aim to
collect quantitative susceptibility data on penicillin and cephalosporins for community
acquired Streptococcus pneumoniae from blood and cerebrospinal fluid; and to
collect data on methicillin resistance for Staphylococcus aureus from blood
cultures.
Organisation
Each participating country has appointed a national representative
microbiologist and a representative epidemiologist. These representatives will also work
together to analyse the data for other epidemiological studies. One of the representatives
from each country acts as the national coordinator. His/her main task is to coordinate
activities of the participating laboratories; arrange distribution and collection of
questionnaires on susceptibility testing; and to collect and forward resistance
data each quarter for international collation. Standardisation and microbiological quality
control methods are being developed in consultation with the European Society of Clinical
Microbiology and Infectious Diseases (ESCMID). EARSS is a component of the
network-of-networks being established by the World Health Organization (WHO) for global
surveillance.
Selection of participating laboratories
EARSS recommended that the national coordinators should select enough
laboratories in their countries to cover at least 20% of the total population. For
community acquired pathogens the catchment population of the laboratories (the number of
people living in the area they serve) will be considered as the denominator. The 400 or so
laboratories participating in EARSS will cover well over 20% of the population in many
countries (figure 1). Most of these laboratories are first-line clinical
laboratories, rather than reference laboratories. Academic and non-academic hospitals are
represented, and the spectrum extends from nursing homes to tertiary referral hospitals.
Epidemiological data
EARSS collects the following information by means of isolate record
forms and questionnaires:
- information about an isolate and its susceptibility test results
- information about patients
- information about the laboratory methods used and denominator data
- data about the hospital(s) served by the laboratory used to generate the denominator.
Isolate record form. This form collects information about
patients and isolates. EARSS requires the following information: sex, month and year of
birth, date of specimen collection, name or code of hospital, hospital department, origin
of patient, isolate specimen number, laboratory code, and antibiotic susceptibility
testing results as specified in the protocol. Furthermore, the isolate record form allows
other optional data to be collected: patient identifier (ID), clinical diagnosis, and
susceptibility for other antibiotics.
Questionnaire on susceptibility testing. This questionnaire asks
about test methods used, and collects denominator data from a laboratory and from the
hospital(s) it serves. The facilities the hospital offers (intensive care unit, renal,
transplant, cardiac surgery) and the number of bed days are requested. For nosocomial pathogens
the number of bed days will be considered as the denominator. Data on patients and
isolates can be related to information about the laboratory and hospital by means of a
unique laboratory code that will be filled out on all isolate record forms and
questionnaires. The authors are aware that the catchment population estimated by a
laboratory may overestimate the true catchment population. True catchment populations can
be calculated using postal codes of the patients from whom isolates are obtained. To
preserve confidentiality this must be done at a national level.
Duplicates
To prevent duplicate isolates from being reported, laboratories are
asked to send information only about the first isolate of each strain from each patient.
These are referred to as ‘patient-isolates’. To be able to correct for duplicate
isolates, the isolate record form asks for patient ID/code. This is marked as optional
information, since in many countries there are legal limitations on the inclusion of
patient identifiers. For the same reason we do not ask for date of birth, but month and
year of birth. A code is needed, however, to exclude duplicates at the national level. If
a patient identifier cannot be used in a particular country, we ask laboratories to use
another (encrypted) code for a specific patient. In countries without legal limitations
the national coordinator will use the patient identifier to exclude repeat isolates,
removing the identifier before sending data to the central database.
Data processing
Participating laboratories are offered two methods of data entry:
electronic and on paper. Details vary from country to country, but if a laboratory opts
for electronic data transfer they can use an existing laboratory information system or
make use of Whonet (and/or Whonet-Baclink). WHO revised the existing microbiology
laboratory database software Whonet4 for EARSS. Laboratories that do not process data
electronically will forward the isolate record forms to their national coordinator, who
will enter the data and send them each quarter to the RIVM in ASCII format. On receipt,
the data will be checked for syntax errors (for example, dates and test results), and
linked to denominator information collected by means of the questionnaire on
susceptibility testing. After this validation, tables, figures, and geographical maps can
be generated and published on an internet site. The aggregated data sets will also be used
for more complex epidemiological studies, for example investigating relationships between
geographical locations and antibiotic resistance.
Feedback
Sufficient and timely feedback is essential for all surveillance
systems. As well as information letters and a newsletter, data will be shared using the
electronic infrastructure ‘Interchange of Data between Administrations’ (IDA)
network of the EU. Within IDA an internet application will be developed to enable
participating laboratories to export their ASCII data to the central EARSS database and to
obtain selected information from the central database.
Quarterly feedback will be given on:
- the total number of S. aureus cases in blood and the proportion that are
methicillin resistant (MRSA)
- prevalence of MRSA cases in blood per 100 patients
- incidence of MRSA cases in blood per 1000 patient days
- prevalence of oxacillin (penicillin) resistance of S. pneumoniae cases in blood
and cerebrospinal fluid
- quarterly incidence of penicillin resistant S. pneumoniae cases in blood and
cerebrospinal fluid per million population during the study.
Results
About 400 laboratories will take part by sending data via national
coordinators to the central EARSS database. Data collection began in some countries on 1
October 1998, and the first results are expected in April 1999. An EARSS manual that is
downloadable from the website has been prepared, and a printed booklet is being
distributed to participating laboratories.
Conclusion
In developing the protocol and questionnaire, the challenge was to
balance scientific validity and feasibility. A first result is that consensus has been
reached by leading microbiologists and epidemiologists on the protocol and logistical
framework. EARSS is already acting as a catalyst for national surveillance systems.
For more information: see the EARSS website (http://www.earss.rivm.nl), contact the
project coordinator Stef Bronzwaer (info.earss@rivm.nl), or a national
coordinator by means of an email addresses on the website.
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