This presentation was delivered as an oral presentation at the ESCP conference in Barcelona in 2014. It was based on a literature review and comparison of wound infection rates in general surgical RCTs. If the SSI is reported as a primary endpoint is was statistically signficantly higher than if it was reported as a secondary endpoint. This is important because it helps to show that studies that report findings that were not the main aim of the study are often flawed and produced a less reliable result. Also means that many wound infection rates that are quoted as potentially far too low and this could impact patient care. This study was done by myself, Shivam Bhanderi, Dmitri Nepogodiev, Stephen Chapman and Aneel Bhangu. https://journals.lww.com/annalsofsurgery/Citation/2016/12000/Underreporting_of_Secondary_Endpoints_in.18.aspx

1. Adequacy of secondary versus primary
assessment of surgical site infection in
randomised controlled trials.
J Matthews, S Bhanderi,
S Chapman, D Nepogodiev, A Bhangu

2. Introduction + Aim
• Surgical Site Infection (SSI) is important1,2
• Common outcome measure in GI surgery RCTs
• SSI rate is very variable - 0<45%3
• RCT outcomes = Accurate, standardised assessment
• Primary and secondary trial outcomes
• Is measuring SSI as a secondary outcome in
RCTs inferior to primary assessment?
1. Kirkland KB, Briggs JP, Trivette SL,WilkinsonWE, SextonDJ. The impact of surgical site infections in the 1990s: attributable mortality, excess length of
hospitalization, and extra costs. Infect Control Hosp Epidemiol. 1999;20(11):725-730.
2. Pinkney TD et al. Impact of wound edge protection devices on surgical site infection after laparotomy: multi centre randomised controlled trial
(ROSSINI trial). BMJ 2013; 347:f4305.
3. Anthony T, Murray BW, Sum-Ping JT, et al. Evaluating an evidence-based bundle for preventing surgical site infection: a randomized trial.Arch Surg.
2011;146(3):263-269.

3. Methods

5. Results – Included Articles
• 61247 articles - 169 RCTs (37,140 patients)
• 32% - Upper gastrointestinal (54/169)
• 30% - Colorectal surgery (51/169)
• 12% - Mixed Upper + Lower (21/169)
• 26% - Appendectomy + Hernia (43/169)
• 82% - Elective surgery (138/169)
• 27% - Primary outcome (45/169)
• 73% - Secondary outcome (124/169)
• 13% - formal definition of SSI (22/169)

6. Results
• Mean SSI rate = 7.1% (Min 0%, Max 35%)
• Primary assessment mean SSI rate = 11.1%
• Secondary assessment mean SSI rate = 5.7%
• Binary logistic regression analysis
• Studies using SSI as a primary outcome measure were more likely to
identify a high (>10%) SSI rate than those reporting it as a secondary
outcome measure (OR 0.30, 95% CI 0.14-0.65, p=0.002)
• When adjusted for contamination, primary assessment of SSI was
associated with an increased chance of high SSI pickup rate compared to
secondary assessment (OR 0.19, 95% CI 0.06-0.69, p=0.011).

7. Conclusion
• Assessment of SSI as a primary outcome in
surgical RCT led to higher pickup rate than
secondary assessment
• Secondary assessment of endpoints should
either be performed to the same standard as
that of primary assessment, or should be
abandoned to prevent underestimation and
save resources.

8. Adequacy of secondary versus primary
assessment of surgical site infection in
randomised controlled trials.
J Matthews, S Bhanderi,
S Chapman, D Nepogodiev, A Bhangu

9. Introduction + Aim
• Surgical Site Infection (SSI) is important
• Patients + Healthcare providers1 + Researchers
• SSI rate - <45%2
• Primary Outcome - Is measuring SSI as a
secondary outcome in RCTs associated with
lower reporting rates than as primary
outcomes reporting?
1. Kirkland KB, Briggs JP, Trivette SL,WilkinsonWE, SextonDJ. The impact of surgical site infections in the 1990s: attributable mortality,
excess length of hospitalization, and extra costs. Infect Control Hosp Epidemiol. 1999;20(11):725-730.
2. Anthony T, Murray BW, Sum-Ping JT, et al. Evaluating an evidence-based bundle for preventing surgical site infection: a randomized
trial.Arch Surg. 2011;146(3):263-269.

10. Total journals in results
n = 1559
Gastrointestinal surgery journals
Impact factor > 3.0
n = 11
01/01/2008 – 31/12/2013
>1000 articles
Structured PubMed Search
Non-gastrointestinal journals
Foreign language GI journals
Impact Factor <3
n = 1548
Article Inclusion Criteria
Randomised Controlled Trial
Laparotomy
Upper, lower, biliary,
appendectomy and hernioplasty161 RCT
Article Exclusion Criteria
Hepatic, renal, GU, vascular
No laparotomy
Article does not mention SSI,
wound infection,
wound complication,
post-operative complication

11. Results – Included Articles
Included Journals Included
Articles
Ann Surg 32
Ann Surg Oncol 3
Arch Surg 14
Br J Surg 36
Dis Colon Rectum 20
J Am Coll Surg 2
JAMA Surg 1
Obes Surg 3
Surg Endosc 32
Surg Obes Relat Dis 5
Surgery 13
Grand Total 161
Surgical
Intervention
No of
Trials
Upper GI 52
Lower GI 50
Mixed GI 16
Appendectomy 11
Hernioplasty 31
Unknown 1
Grand Total 161
Timing of
Intervention
No of
Trials
Elective 130
Emergency 10
Mixed 10
Unknown 11
Grand Total 161

12. Result – Primary Outcome
• Mean SSI rate = 7.02% (Min 0%, Max 35%)
• Primary assessment mean SSI rate = 11.1%
• Secondary assessment mean SSI rate = 5.7%
• Binary regression analysis p<0.01

13. Results – Secondary Outcomes
Definition Included
No of
Articles
(%)
CDC/ ASEPSIS 17 10.56
Other 31 19.25
None 113 70.19
Grand Total 161 100
Outcome
Measure
No of
articles
(%)
Primary 40 24.84
Secondary 121 75.16
Grand
Total
161 100.00
No of Articles
(%)
Clearly
Documented
SSI
126 78.26
Poorly
Documented
35 21.74
Grand Total 161 100.00

14. Conclusion
• Secondary assessment of endpoints should
either be performed to the same standard as
that of primary assessment, or should be
abandoned to prevent underestimation and
save resources.