Point prevalence survey epidemiology Facilitator notes: Epidemiological methods for point prevalence surveys of healthcare-associated infections and antimicrobial use in acute care hospitals Point prevalence survey epidemiology Version 2017 Revision: 2018

Objectives Specific objectives of this session: Describe the principles and approaches to PPS epidemiology inclusive of strengths and limitations Understand the concept of reliability in the context of the ECDC PPS Understand reporting output from the ECDC PPS These are similar to the general course objectives Facilitator notes:

Outline This session consists of the following elements Prevalence and incidence What are prevalence and incidence? Relationship between prevalence and incidence Prevalence or incidence? Numerators and denominators Using local PPS data to inform practice Also on ward-level 4. Validity and reliability What are validity and reliability? ECDC PPS methods for testing validity and reliability Facilitator notes:

Prevalence and Incidence

What is Prevalence? Number of affected individuals present in a population at a specific point in time. Presented as a proportion or percentage of all individuals in the population at that point in time. Example: Prevalence of HAI Survey population = 100 For each patient: Does the patient currently have an HAI? If 5 patients have an HAI at the time of survey, prevalence = 5/100= 5% Facilitator notes:

What is Prevalence? Prevalence of antimicrobial prescribing Survey population = 500 For each patient: Is the patient currently receiving an antimicrobial? If 150 patients are receiving an antimicrobial at the time of survey, prevalence = 150/500= 30% Prevalence of invasive device use Survey population = 1000 For each patient: Does the patient currently have a device in situ? If 30 of these patients have a central vascular catheter (CVC) in situ at the time of survey, what would the prevalence of CVC use be calculated as in the survey population? Facilitator notes:

What is Incidence? The number of new cases occurring in a population at risk over a defined period of time. Presented as the percentage or proportion of those “at risk” that go on to develop the outcome. Requires patients without the outcome (e.g. HAI) to be followed over time to determine whether they develop the outcome. Facilitator notes:

Examples of Incidence Incidence of surgical site infection (SSI) There were 45 new cases of SSI following 1000 caesarean section procedures during 2008. Incidence of SSI = 45/1000= 4.5% during 2008 Incidence of catheter-associated urinary tract infection (CAUTI) There were 14 new cases of CAUTI in a population of 100 patients catheterised between January to March 2010. What is the incidence of CAUTI between January and March 2010? Facilitator notes:

Prevalence or Incidence Quick and relatively easy to perform Can measure the burden of all HAI types (not only those included in incidence surveillance) ONLY represents the situation at the time of survey (sample of one of many survey days) Cannot measure risk of HAI, monitor trends in HAI or identify HAI outbreaks Repeated prevalence surveys can also enable to interpret even weak trends Incidence Resource and labour intensive Can measure risk of HAI Can monitor trends and identify outbreaks Facilitator notes:

Excercises

Prevalence and Incidence Jan 2017 Dec 2017 May Sept Case 7 Case 6 Case 5 Case 4 Case 3 Case 2 Case 1 Notes to trainer: This diagram represents cases of infection during the period January 2009 to December 2009. You should demonstrate the course of infection using the following examples… Case 1 developed before January 2009 and was ongoing until just after September 2009. Case 5 developed in April 2009 and was ongoing until July 2009. Now stop the presentation and ask the participants to work in small groups to answer the questions on the slides. Solutions- Question 1- Any cases occurring after January 2009= 5 Incidence= 5/100=5% Question 2- four existing cases of infection present in May 2009. Prevalence= 4/30= 13.3% Question 3- four existing cases of infection present in September 2009. Prevalence= 4/36=11.1% PPS performed How many new cases developed between January and December 2017? If there were a total of 100 “at risk” patients between January and December 2017, what is the incidence of infection? How many existing cases of infection were prevalent at the May PPS? If 30 patients were surveyed in May, what was the prevalence of infection? How many existing cases of infection were prevalent at the September PPS? If 36 patients were surveyed in September, what was the prevalence of infection?

Prevalence and Incidence HAI Case Recovery or death or discharge Incidence No HAI Prevalence Facilitator notes:

Numerators and denominators for the ECDC PPS

Measuring prevalence Prevalence = numerator/denominator Numerator Number of patients on the ward with active infection at the time of survey Denominator Number of patients on the ward at 8am on the morning of the survey Data collector visits a ward where there were 27 patients present at 8:00 AM on the morning of the survey. After carrying out the survey, 4 patients were identified as having active infection. Denominator is 27 Numerator is 4 Prevalence = 4/27 = 15% Facilitator notes:

Using local PPS data to inform practice

Local PPS data Opportunity with collection of local data to inform practice at a local level as well as national and European level. Local PPS data can be used to Compare the structure and process indicators to national and European level Identify targets for quality improvement Evaluate effect of interventions (in repeated PPS) Requires caution due to small sample size and survey day being a sample of all possible survey days. Especial caution when interpreting results for individual wards. Facilitator notes:

Validity and reliability

Validity What is validity? Measure of ability of a data collector to distinguish between who has a HAI and who does not. Data collected are compared with „gold standard” data collection. Validation exercises check whether the data collector is correctly applying the case definitions, for example: Patient has had surgery 5 days ago, and has S. aureus isolated from an aseptically obtained fluid from the superficial incision. Data collector decides “No surgical site infection (SSI)”, the gold standard decides “Superficial SSI”. Different answers to the same question! The data collector’s decision is not valid when compared with the gold standard data collector Facilitator notes:

Reliability What is reliability? Measure of repeatability of HAI diagnosis by data collectors Measures the agreement of diagnosis between data collectors Reliability exercises check that the data collectors are applying the definitions consistently each time, for example: 10 data collectors collect data from the same patient 9 data collectors decide “No urinary tract infection (UTI)” 1 data collector decides “UTI” Different answers to the same question The data collectors are not applying the case definitions consistently so the results are not reliable Facilitator notes:

Validity and reliability VALID AND RELIABLE RELIABLE NOT VALID NOT RELIABLE OR VALID 5 data collectors All 5 diagnose SSI-S Gold standard- SSI-S 7 data collectors All diagnose SSI-S Gold standard- SSI-D 11 data collectors 5 diagnose BRON 2 diagnose PN1 3 diagnose PN4 1 diagnose no HAI Gold standard - No HAI Notes to trainer: This diagram demonstrates validity and reliability. The data collectors all collect data on the same patient and their diagnosis of HAI is compared. Explanation of the diagram VALID and RELIABLE- the data collector is applying the definitions in a consistent and correct manner. Example: 5 data collectors- all consistently diagnose SSI agreeing with the gold standard RELIABLE not VALID- the data collector is applying the definitions incorrectly in the same way every time. Example: 7 data collectors- all consistently diagnose superficial SSI but the gold standard data collector has diagnosed a deep SSI NOT RELIABLE or VALID- the data collector is not applying the definitions in the same way or correctly each time. Example: 11 data collectors- there is no consistency in the diagnosis of HAI with several different respiratory infections being diagnosed. Only one data collector has reached the same decision as the gold standard data collector of NO HAI

ECDC PPS 2016-2017 Validation All Member States are expected to perform a validation study of their national or regional PPS: at the same time as a national or regional PPS by a national/regional PPS validation team a minimum sample of 5 hospitals and 250 patients a recommended sample of 25 hospitals and 750 patients The current protocol is the ECDC PPS validation protocol v3.1 National PPS coordinating centre will select and further inform the selected hospitals Facilitator notes:

ECDC PPS 2016-2017 Validation The objectives of the validation: to assess the validity, reliability and inter-country comparability of the data to assess the data accuracy of selected hospital process and structure indicators Facilitator notes:

In summary List of learning points in this session: 1. Point prevalence surveys are an important methodology for: Measuring the burden of HAI and antimicrobial use Describing the prevalence of all HAI types Informing priority setting at a local, national and European level A consistent and robust approach is essential to ensuring the validity and reliability of the results Facilitator notes:

Facilitator notes: Acknowledgements The creation of this training material was commissioned in 2010 by ECDC to Health Protection Agency (UK) with the direct involvement of Dr. S. Hopkins, Prof. J. Reilly, S. Cairns, Dr. E. Sheridan, Dr. G. Hughes, Prof. B. Cookson, Dr. A. Charlett, G. Kafatos, B. Muller Pebody, F. Cowan, and Y. Sueiro. The revision and update of this training material was commissioned in 2017 by ECDC to Transmissible (NL) with the direct involvement of Dr. Arnold Bosman and Dr. Ágnes Hajdu