Bacterial Species and Load Increase During Negative Pressure Wound Therapy

A Prospective Cohort Study

Kelly Aranka Ayli Kwa, MD; Pieta Krijnen, PhD; Alexandra T. Bernards, MD, PhD; Inger B. Schipper, MD, PhD; Annebeth Meij-de Vries, MD, PhD; Roelf S. Breederveld, MD, PhD


Wounds. 2020;32(3):74-80. 

In This Article

Abstract and Introduction


Introduction: The course of both the bacterial species and load and the incidence of infection during negative pressure wound therapy (NPWT) are unclear, with published studies presenting contradicting results.

Objective: The aim of the study is to assess the changes in both bacterial species and load, as well as the incidence of infection, before and after NPWT in a patient population with a variety of wounds.

Methods: Surgical patients 18 years of age or older who needed NPWT were included in this multicenter, prospective cohort study. A wound swab culture was taken before NPWT and either immediately following NPWT or 6 weeks of follow-up. The change of bacterial species, bacterial load, and rate of infection were determined before and after the start of NPWT.

Results: In total, 104 patients were analyzed. The number of positive cultures increased from pre- to post-NPWT. The most cultured pathogenic bacterium was Staphylococcus aureus. The bacterial load was moderately higher at the end of NPWT than at the start (P < .0001). It was noted that 2 swabs contained multidrug-resistant bacteria, 1 pre-NPWT and 1 post-NPWT. Prior to NPWT, 26 patients had a wound infection, 5 of which had a persisting infection at the end of the study. Post-NPWT, 14 patients developed a wound infection.

Conclusions: The number of S aureus strains and overall bacterial load increased during NPWT, and the incidence of infection remained the same. Further studies should be conducted to determine whether the increase in bacterial load influences other wound outcome parameters.


Negative pressure wound therapy (NPWT) was first described by Fleischmann et al in 1993.[1,2] It entails the introduction of a subatmospheric pressure, produced by suction through a tube, to a dressing foam or gauze, which covers the wound bed. This can be carried out with the use of a NPWT system (V.A.C. Therapy; KCI, San Antonio, TX), that delivers continuous or intermittent negative pressure to the wound bed. The introduction of NPWT took place in Europe in 1994,[3] and an overview of studies of its first implications in various wounds were published by Argenta[4] and Morkykwas[5] in 1997. Negative pressure wound therapy is used to promote granulation tissue formation and accelerate wound healing; it reduces edema, increases tissue perfusion, and may prevent infection.[6–9] Several studies[10–12] have shown NPWT can be safely applied in infected wounds after debridement. It can be used in a variety of wound types, including acute, chronic, traumatic, and surgical, as well as for flap surgery and skin grafts, in diverse anatomical locations.[13,14]

However, the bacterial growth or clearance in the wound during NPWT remains a complex matter. Despite reports indicating NPWT can achieve bacterial clearance and prevent infection, the change of the bacterial species and load during NPWT is still unclear, and studies have published contradictory results.[15,16] Several studies[5,17,18] reported a positive influence of NPWT (eg, clearance or reduction of bacteria), while other studies[19–22] reported a stable or even increase of bacterial growth in NPWT. The systematic review by Glass et al[16] indicates the general belief that NPWT suppresses bacterial growth is an oversimplification, and the change in bacterial load is likely to be species-specific. Of note, 2 clinical studies[20,23] examined the change of bacterial species during NPWT and showed contradictory results in the shifts of bacterial species; Mouës et al[20] studied a relatively small group of patients (N = 29), in which the type of antibiotics used was not specified, and the other study by Jentzsch et al[23] only involved patients in a trauma center.

The primary objective of this study was to determine the change in bacterial species and load, as well as the incidence of infection, before and after NPWT, in patients with various types of wounds. Furthermore, the course of wound infections during NPWT were evaluated.