Editorials
Positive Pocket Cultures From Cardiac Implantable Electrophysiological Devices Without Infection – Contamination or Colonization? –
2015 Volume 79 Issue 8 Pages 1680-1681
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2015 Volume 79 Issue 8 Pages 1680-1681
Infections related to cardiac implantable electrophysiological devices (CIEDs) have increased, owing to expanded functions and indications of the devices.1 The CIED infections, however, can be difficult to diagnose because echocardiography is less accurate, blood cultures are less sensitive and the diagnosis is hardly considered. Furthermore, the CIED infections are also complex to manage because a removal of the infected devices can be a major procedure with a risk of death or serious complications.2
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Current guidelines recommend avoiding taking pocket cultures from patients without clinical evidence of CIED infection because the positive results may lead to unnecessary antimicrobial therapy or surgery.2,3 This is based on an assumption that contamination is likely to result in false positive. However, previous studies have reported that the asymptomatic colonization of CIEDs might change into the symptomatic CIED infection.4–7 The current guidelines do not resolve this problem because those previous studies have lacked control groups of patients to differentiate contamination from colonization.
In this issue of the Journal, Okada et al8 investigate the hypothesis of positive pocket cultures without signs of CIED infection and its clinical implication. They took pocket cultures from new implantations as control samples of contaminated bacteria (false positive) to uncover colonized bacteria (true positive) in the replacement device. A key to differentiating colonization from contamination is a positive ratio of the pocket cultures; a colonized sample contains a larger number of bacteria than a contaminated sample.9,10 A series of 100 consecutive patients who underwent pacemaker implantation were included in this prospective observational study conducted in a single medical center in Japan. The positive ratio of pocket culture (6 samples/patient) was compared between 49 new implantations and 51 replacements. The pocket cultures were positive in 272 (45%) of 600 samples, while smear samples were all negative. The majority of the cultured bacteria were Propionibacterium species (42%) followed by coagulase-negative staphylococci (8%). The positive ratios were not different between new implantations and replacements for Propionibacterium species (45% vs. 47%, P=0.8) and for coagulase-negative staphylococci (14% vs. 24%, P=0.1). During a mean follow-up period of 25±3 months, only 1 patient developed a CIED infection at 13 months after the device replacement, with a different bacterial result from the prior sampling.
The issue of positive pocket cultures from CIEDs without infection has been addressed by 4 other groups (Table). Pichlmaier et al4 identified bacterial DNA in 27% of biofilm samples from the pocket of removed devices for replacement. During a median follow-up period of 25 months, no patients developed subsequent CIED infection. Kleemann et al5 identified bacteria in 33% of swab cultures from the pocket of removed devices for replacement. During a median follow-up period of 7 months, 7.5% of the culture-positive patients developed a subsequent CIED infection with the same species of microorganism. Rohacek et al6 identified bacteria in 38% of fluid cultures from sonicated devices removed for replacement. During a mean follow-up period of 18 months, 4.5% of the culture-positive patients developed a subsequent CIED infection with the same species of microorganism. Mason et al7 identified bacteria in 21% of cultures using 3 different modalities (swab, sanitation fluid, and tissue) from removed devices and their pockets. During a mean follow-up period of 10 months, no patients developed subsequent CIED infections. Bacteria can be cultured from the pocket of a removed device for replacement in a significant proportion of asymptomatic patients; they may cause subsequent CIED infection at a later stage.
| Investigators | Year | No. of samples per patient (types of samples) |
Patients without CIED infection, n |
Positive culture, n (%) |
Propionibacterium species, n |
Coagulase- negative staphylococci, n |
Staphylococcus aureus, n |
Subsequent CIED infection, n (%) |
Follow-up period, months |
|---|---|---|---|---|---|---|---|---|---|
| Pichlmaier et al4 |
2008 | 1 (biofilm) | 108 | 29 (27) | ND | ND | 0 | 0/29 (0.0) | 25 (median) |
| Kleemann et al5 |
2010 | 1–3 (swab, leads) |
122 | 40 (33) | 7 | 27 | 1 | 3/40 (7.5) | 7 (median) |
| Rohacek et al6 |
2010 | 2 (sonication fluid, swab) |
115 | 44 (38) | 27 | 11 | 0 | 2/44 (4.5) | 18 (mean) |
| Mason et al7 |
2011 | 3 (sonication fluid, swab, tissue) |
66 | 14 (21) | 7 | 2 | 0 | 0/14 (0.0) | 10 (mean) |
| Okada et al8 |
2015 | 6 (swab for all samples) |
100 | 55 (55) | 36 | 19 | 0 | 1/55 (1.8) | 13 (mean) |
CIED, cardiac implantable electrophysiological devices; ND, not described.
What is the role of bacteria cultured from CIED pockets without infection? It has been an assumption that an asymptomatic colonization could be sustained by a balance between host immunity and microorganisms.11 Okada et al suggest that positive cultures might be a merely contamination during operation, rather than asymptomatic contamination, by demonstrating the comparable positive ratio of bacteria cultured from new and replacement devices.8 This suggestion well explains the relatively low ratio of subsequent CIED infection despite the high incidence of positive bacterial results from the pocket cultures and comparable incidence of CIED infection between patients with positive and negative cultures.5
The majority of CIED infections are caused by either Staphylococcus aureus (S. aureus) or coagulase-negative staphylococci; Propionibacterium acnes is commonly isolated from pocket cultures without CIED infections.6,12 It might be reasonable to regard Propionibacterium species cultured from CIED pockets in asymptomatic patients as contaminating bacteria, which would not cause subsequent CIED infection. S. aureus and coagulase-negative staphylococci, however, can cause subsequent CIED infection, even if they are cultured from non-infected devices – subsequent CIED infection occurred in one of 1 patients with positive S. aureus, and 2 of 27, and 2 of 11 patients with positive coagulase-negative staphylococci.5,6
Therefore, active investigation of CIED infections might be recommended even in asymptomatic patients, when pocket cultures detect S. aureus or coagulase-negative staphylococci. Contamination (a useless marker of future infection) is a common cause of positive pocket culture in asymptomatic patients; however, it likely masks the asymptomatic colonization, which may represent an early stage of CIED infection. Further studies should proceed to clarify the pathogenic mechanisms of developing CIED infections and to define the subset of asymptomatic colonization representing subsequent CIED infections.
All authors report no conflicts of interest.
