Space-Time Relations of
Clostridium difficile cases within
a health economy:
A Social Network Analysis
Presented by Mark Reacher network analysis by Iain Roddick
Wendy Rice, Rowan Slowther, Judy Ames, Giri Shankar
Clostridium difficile natural history
• A common antibiotic associated infectious diarrhoea
• Transmission by ingestion of toxin producing spores in
faeces of an infected case.
• Spores may remain “dormant” in large gut as part of
microbiota until …..
• Antibiotic treatment perturbs large gut microflora, spores
no longer held in check and proliferate causing
Clostridium difficile Associated Disease
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Space-Time Relations of Clostridium difficile cases within a health economy:
A Social Network Analysis
Clostridium difficile Associated Disease (CTAD)
Comprises a wide range of illness from self
limiting diarrhoea to severe protracted
diarrhoea, fluid loss , toxic shock, toxic
megacolon (requiring life saving
colectomy) and acute death.
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Clostridium difficile control
• Universal infection control essential including hand
hygiene in care staff : cleaning lavatories and all
sanitation surfaces wards and fomites - oxidising
disinfectants as well as physical cleaning with detergent
required to destroy spores
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BBC Friday, 5 November, 2004
Hospital superbug must be
halved. Bloodstream infections
with the hospital superbug
MRSA must be halved in three
years, the government has
said. Health Secretary John
Reid tasked NHS hospitals
with achieving a year on year
reduction up to and beyond
March 2008.
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Development of Health care associated
infections Mandatory surveillance
2004 April CDI > 65 years; MRSA bacteraemia
2005 April Enhanced MRSA bacteraemia
2007 April CDI > 2 years
2011 January MSSA and E.coli bacteraemia
added
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Attributing site of acquisition of infection
Cases of Clostridium difficile infection occurring
within 72 hours of admission have been
regarded as acquiring infection prior to
admission to that hospital – at another hospital
or in the community
Hospitals have only been held accountable for
infections occurring greater than 72 hours
following admission
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Clostridium difficile reports mandatory surveillance 2007
to 2013 in England
60000
50000
40000
Total
30000
Trust apportioned
20000
10000
0
2007-8
8
2008-9
2009-10
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2010-11
2011-12
2012-13
Examination of space time relations of
Community attributed Clostridium difficile
cases
A substantial proportion of Clostridium difficile cases arising
in the North Norfolk health economy were attributed to
acquisition in the community
Community health services in Norfolk recorded the dates of
arrival and discharge in care settings and to home for all
new cases of Clostridium difficile infection diagnosed by
GP testing in the community over a two year period
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The Norfolk Community attributed Clostridium
difficile cases
• 199 county residents who had samples submitted by a GP
and tested positive for C.difficile between 2010-2012
• 78 had been admitted at least once to Hospital A
• 40 had been admitted at least once to Hospital B
• No cases had been admitted to both hospitals
• 26 cases had been to Care Homes with at least one other
resident case
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Space-Time Relations of Clostridium difficile cases within a health economy:
A Social Network Analysis
Social Network Analysis (SNA)
• The methods have their roots in the work of 18th
Century mathematicians on Graph Theory
• Focuses on relationships between individuals rather
than their attributes
• Applied in a wide variety of scientific research –
e.g. genetics, linguistics, electrical engineering,
sociology
• Advances in computing power and availability of
software have made it easier to apply SNA to a wide
range of problems outside of formal research
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Space-Time Relations of Clostridium difficile cases within a health economy:
A Social Network Analysis
Data & Software
• Very simple dataset – Just 5 data fields, captured
in Excel:
PatientID
Location
Start Date
End Date
1st Positive Specimen Date
Procedures written in SQL Server to
a) detect space-time coincidences between people
in the cohort
b) Measure time spent at risk of infection
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Space-Time Relations of Clostridium difficile cases within a health economy:
A Social Network Analysis
Co-location
of people
Hospital A
CARE
HOME
Hospital B
C.diffiicile status
not considered
85 of 199 people
did spend some
time together
CARE
HOME
CH
…in 2 hospitals,
and in 5 care
homes
B
CH + B
A
CARE
HOMES:
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Space-Time Relations of Clostridium difficile cases within a health economy:
A Social Network Analysis
Hospital A –
Who spent
Taking
C.difficile
time with
status
who?
into consideration –
Who wasspecimens
Positive
at risk? not
taken into account
Arrow direction represents
possiblelines
Joining
transmission
represent
co-location for 1 or more
Arrow size is indicative of
days
Number of Days at Risk
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Space-Time Relations of Clostridium difficile cases within a health economy:
A Social Network Analysis
CARE
HOME
Conclusions
• Most community diagnosed Clostridium difficile infections
had space time overlaps with earlier onset cases at their local
hospital
•The “72 hour rule” of attributing cases to community
acquisition denies the centrality of hospital transmission
•Higher levels of infection control are still urgently needed in
hospitals to contain the continuing risk of Clostridium difficile
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Space-Time Relations of Clostridium difficile cases within a health economy:
A Social Network Analysis
Acknowledgements
Alongside my co-authors I’d like to acknowledge the
contributions of
The Norfolk Health System HCAI Group, and
Mr. Steven Martin of Cambridge Institute of Public Health
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Space-Time Relations of Clostridium difficile cases within a health economy:
A Social Network Analysis