A Preventive “Number Needed to Screen” Would Have Been More Relevant

Letters to the Editor Screening for Methicillin-Resistant Staphylococcus Aureus—an Analysis Based on Findings From the Hospital Infection Surveillance System (KISS) Dr. med. Miriam Wiese-Posselt, MPH, Selin Saydan, Dr. rer. medic. Frank Schwab, et al. in Heft 26/2023

The prevalence and nosocomial incidence of MRSA have decreased substantially in recent years, especially during the SARS-CoV-2 pandemic (1). This decrease may also partly be due to stricter general hygiene measures during the pandemic, as is also being discussed for other nosocomial infections (2). As is known from diagnostic testing of blood cultures, no substantial gain in detecting bloodstream infections is made if blood culture rates increase further (3). This has also been shown for MRSA screening. The nosocomial transmission probability of MRSA in hospitals with a lower rate of nasal swabs is not increased (1). Because of the non-existent preventive effect and the high resource use as a result of a high screening frequency, a more targeted screening strategy for MRSA has been recommended (1). Instead of the screening rate it would be more helpful to determine how many patients would have to be screened to detect one positive case of MRSA (“number needed to screen,” NNS). On the basis of the data (1) an NNS between 97 (95% confidence interval [94; 99]) and 186 ([183; 188]) can be calculated for the 16 years under study. This metric may enable clinicians to assess and adapt any MRSA strategy more effectively on location. For MRSA, NNS depending on institution and patient have been described with a range of 84–462 (mean between 102 and 259) (4). More relevant than the NNS itself seems to be the determination of a “preventive” NNS: How many patients have to be screened in order to maintain the low nosocomial incidence density of currently 0.04/1000 patient days (1)? The authors could try to determine this on the basis of the datasets and subsequent filing.

DOI: 10.3238/arztebl.m2023.0206

PD Dr. med. habil. Enrico Schalk

Otto-von-Guericke-Universität Magdeburg, Medizinische Fakultät,

Klinik für Hämatologie und Onkologie, [e-mail]

References

1. Wiese-Posselt M, Saydan S, Schwab F, et al.: Screening for methicillin-resistant Staphylococcus aureus—an analysis based on findings from the Hospital Infection Surveillance System (KISS), 2006–2021. Dtsch Arztebl Int 2023; 120: 447–53

2. Schalk E, Schmitt T, Panse J, et al.: Central venous catheter-related bloodstream infections in patients with haematological malignancies during the SARS-CoV-2 pandemic. Br J Haematol 2022; 199: e16–e20

3. Karch A, Castell S, Schwab F, et al.: Proposing an empirically justified reference threshold for blood culture sampling rates in intensive care units. J Clin Microbiol 2015; 53: 648–52

4. Fuller C, Robotham J, Savage J, et al.: The national one week prevalence audit of universal meticillin-resistant Staphylococcus aureus (MRSA) admission screening 2012. PLoS One 2013; 8: e74219