Carriage of methicillin-resistant Staphylococcus aureus in children <6 years old: a retrospective follow-up study of the natural course and effectiveness of decolonization treatment.

BACKGROUND: Decolonization treatment of MRSA carriers is recommended in Denmark, except in households with MRSA-positive children <2 years old (wait-and-see approach). OBJECTIVES: To investigate a wait-and-see approach in children 2-5 years old, and the effect of decolonization treatment of MRSA carriage in all children <6 years old. PATIENTS AND METHODS: In this retrospective follow-up study, we included MRSA carriers <6 years old in the Capital Region of Denmark from 2007 to 2021. Data were collected from laboratory information systems and electronic patient records. We divided children into age groups of <2 years or 2-5 years and decolonization treatment versus no treatment. Treatment was chlorhexidine body washes and nasal mupirocin, sometimes supplemented with systemic antibiotics. Children were followed until becoming MRSA free, or censoring. The probability of becoming MRSA free was investigated with Cox regression (higher HRs indicate faster decolonization). RESULTS: Of 348 included children, 226 were <2 years old [56/226 (25%) received treatment] and 122 were 2-5 years old [90/122 (74%) received treatment]. Multivariable analyses did not show a larger effect of decolonization treatment versus no treatment in <2-year-olds (HR 0.92, 95% CI 0.52-1.65) or 2-5-year-olds (HR 0.54, 95% CI 0.26-1.12). Without treatment, 2-5-year-olds tended to clear MRSA faster than <2-year-olds (HR 1.81, 95% CI 0.98-3.37). CONCLUSIONS: We did not find a larger effect of decolonization treatment versus no treatment in children <6 years old, and 2-5-year-olds tended to become MRSA free faster than <2-year-olds. These results support a wait-and-see approach for all children <6 years old, but further studies are needed.

Mortality and exacerbations associated with Stenotrophomonas maltophilia in chronic obstructive pulmonary disease. A regional cohort study of 22,689 outpatients.

OBJECTIVES: The clinical significance of Stenotrophomonas maltophilia in patients with COPD is poorly understood. We aimed to determine whether a lower respiratory tract culture positive for S. maltophilia in COPD patients was independently associated with increased risk of death and hospitalisation for exacerbation of COPD. METHODS: An observational cohort study following outpatients with COPD in Eastern Denmark between 2010 and 2018, with a follow-up period of five years. Presence of S. maltophilia was treated as a time-varying exposure, where patients were considered exposed at the time of the first isolation of S. maltophilia from the lower respiratory tract. The hazard ratio (HR) of death and hospitalisation for acute exacerbations of COPD was assessed using a Cox proportional hazards regression. RESULTS: Of the total 22,689 patients 459 (2.0%) had a lower respiratory sample positive for S. maltophilia. A total of 7,649 deaths (S. maltophilia positive: 243 (52.9%) and S. maltophilia negative: 7,406 (34.4%)) and 24,912 hospitalisations for exacerbation of COPD (S. maltophilia positive: 1,100 in 459 patients and S. maltophilia negative: 23,821 in 22,230 patients) were registered during the study period. We found that a lower respiratory tract culture positive for S. maltophilia was associated with both increased mortality: HR 3.3 (95% CI 2.6-4.3), and hospitalisation for exacerbation of COPD: HR 3.4 (95% CI 2.8-4.1). CONCLUSIONS: A lower respiratory tract culture positive for S. maltophilia in COPD patients was associated with a substantially increased mortality and hospitalisation for exacerbation of COPD. Randomised controlled trials are proposed to determine whether S. maltophilia should be the target of antibiotic treatment.

Delabeling of Penicillin Allergy: Room for Improvement.

BACKGROUND: Penicillin allergy labels have been shown to be associated with suboptimal treatment, negative health outcomes, and increased antibiotic resistance. Many inpatients claim to have penicillin allergy, but studies show that allergy can be disproved and the label removed in up to 90% of cases. OBJECTIVES: The purpose of the study was to investigate the proportion of patients with a penicillin allergy label in a Danish hospital and to classify patients according to the risk of having penicillin allergy in "no risk," low, and high risk. METHODS: For 22 days, inpatients with penicillin allergy labels were interviewed, had their dispensed penicillin prescriptions examined, and were subsequently categorized into risk groups based on the risk evaluation criteria in national guidelines. RESULTS: In total, 260 patients had a penicillin allergy label (10% of the inpatients). Out of 151 included patients, 25 were "no risk" patients (17%), who could potentially have their penicillin allergy label removed without testing. 42 were low-risk patients (28%). 10 "no risk" patients and 20 low-risk patients had been prescribed and dispensed one or more penicillins despite an allergy label. CONCLUSION: Ten percent of inpatients have a penicillin allergy label in a Danish hospital. 17% of these could potentially have their penicillin allergy label removed without allergy testing.

Streptococcal species as a prognostic factor for mortality in patients with streptococcal bloodstream infections.

PURPOSE: Streptococcal bloodstream infections (BSIs) are common, yet prognostic factors are poorly investigated. We aimed to investigate the mortality according to streptococcal species and seasonal variation. METHODS: Patients with streptococcal BSIs from 2008 to 2017 in the Capital Region of Denmark were investigated, and data were crosslinked with nationwide registers for the identification of comorbidities. A multivariable logistic regression analysis was performed to assess mortality according to streptococcal species and season of infection. RESULTS: Among 6095 patients with a streptococcal BSI (mean age 68.1 years), the 30-day mortality was 16.1% and the one-year mortality was 31.5%. With S. pneumoniae as a reference, S. vestibularis was associated with a higher adjusted mortality both within 30 days (odds ratio (OR) 2.89 [95% confidence interval (CI) 1.20-6.95]) and one year (OR 4.09 [95% CI 1.70-9.48]). One-year mortality was also higher in S. thermophilus, S. constellatus, S. parasanguinis, S. salivarius, S. anginosus, and S. mitis/oralis. However, S. mutans was associated with a lower one-year mortality OR 0.44 [95% CI 0.20-0.97], while S. gallolyticus was associated with both a lower 30-day (OR 0.42 [95% CI 0.26-0.67]) and one-year mortality (OR 0.66 [95% CI 0.48-0.93]). Furthermore, with infection in the summer as a reference, patients infected in the winter and autumn had a higher association with 30-day mortality. CONCLUSIONS: The mortality in patients with streptococcal BSI was associated with streptococcal species. Further, patients with streptococcal BSIs infected in the autumn and winter had a higher risk of death within 30 days, compared with patients infected in the summer.

Use of inhaled corticosteroids and risk of acquiring Pseudomonas aeruginosa in patients with chronic obstructive pulmonary disease.

BACKGROUND: Inhaled corticosteroids (ICS) are commonly used to treat COPD and are associated with increased risk of pneumonia. The aim of this study was to assess if accumulated use of ICS is associated with a dose-dependent risk of a positive airway culture with Pseudomonas aeruginosa in patients with COPD. METHODS: We conducted a multiregional epidemiological cohort study including Danish COPD patients followed in outpatient clinics during 2010-2017. ICS use was categorised based on accumulated prescriptions redeemed 365 days prior to cohort entry. Cox proportional hazard regression model was used to estimate the risk of acquiring P. aeruginosa. Propensity score matched models were used as sensitivity analyses. RESULTS: A total of 21 408 patients were included in the study, of which 763 (3.6%) acquired P. aeruginosa during follow-up. ICS use was associated with a dose-dependent risk of P. aeruginosa (low ICS dose: HR 1.38, 95% CI 1.03 to 1.84, p=0.03; moderate ICS dose: HR 2.16, 95% CI 1.63 to 2.85, p<0.0001; high ICS dose: HR 3.58, 95% CI 2.75 to 4.65, p<0.0001; reference: no ICS use). A propensity matched model confirmed the results (high ICS dose compared with no/low/moderate ICS dose: HR 2.05, 95% CI 1.76 to 2.39, p p<0.0001). CONCLUSION: Use of ICS in patients with COPD followed in Danish outpatient clinics was associated with a substantially increased and dose-dependent risk of acquiring P. aeruginosa. Caution should be taken when administering high doses of ICS in severely ill patients with COPD. These results should be confirmed in comparable cohorts and other settings.

Safe De-Labeling of Patients at Low Risk of Penicillin Allergy in Denmark.

INTRODUCTION: Penicillin allergy is suspected in 10% of hospital inpatients but can be disproved in 90% of cases. Direct oral provocation without preceding tests among low-risk patients has proven to be safe in studies of both children and adults and is gaining use across the world. The aims of this study were to investigate the rate of severe allergic reactions to direct oral drug provocation, without preceding tests, in penicillin allergy patients stratified to be at low risk, as well as to examine if these patients have barriers to penicillin allergy de-labeling and future use of penicillins. METHODS: Adult patients referred to a university hospital allergy clinic with a suspected penicillin allergy were prospectively risk evaluated. Patients stratified to be at low risk were offered a direct oral provocation with a single-dose amoxicillin followed by 4 days of continued treatment. The same risk stratification criteria were applied to a larger retrospective cohort. RESULTS: In the prospective study population, 202 patients had a direct oral drug provocation and 20 (10%) were positive. There were no cases of anaphylaxis or severe delayed hypersensitivity. Fifteen reactions were benign rashes with onset >1 day after initial dosing, and 13 of these were maculopapular rashes. The same low-risk criteria were applied retrospectively to patients in a drug provocation database, and 1,759 patients fulfilled the criteria; of these, 10% had positive provocations, and there were no cases of anaphylaxis or severe delayed hypersensitivity. De-labeled patients in the prospective study reported not to fear future penicillin intake, after prolonged provocation. CONCLUSION: The risk stratification criteria for identifying low-risk patients for the oral drug provocation test without prior skin testing were safe in terms of avoiding anaphylaxis or severe delayed hypersensitivity. Benign delayed skin reactions still occurred, and access to allergy advice and follow-up is necessary.

Prevalence of Infective Endocarditis in Streptococcal Bloodstream Infections Is Dependent on Streptococcal Species.

BACKGROUND: Streptococci frequently cause infective endocarditis (IE), yet the prevalence of IE in patients with bloodstream infections (BSIs) caused by different streptococcal species is unknown. We aimed to investigate the prevalence of IE at species level in patients with streptococcal BSIs. METHODS: We investigated all patients with streptococcal BSIs, from 2008 to 2017, in the Capital Region of Denmark. Data were crosslinked with Danish nationwide registries for identification of concomitant hospitalization with IE. In a multivariable logistic regression analysis, we investigated the risk of IE according to streptococcal species adjusted for age, sex, ≥3 positive blood culture bottles, native valve disease, prosthetic valve, previous IE, and cardiac device. RESULTS: Among 6506 cases with streptococcal BSIs (mean age 68.1 years [SD 16.2], 52.8% men) the IE prevalence was 7.1% (95% CI, 6.5-7.8). The lowest IE prevalence was found with Streptococcus pneumoniae (S pneumoniae) 1.2% (0.8-1.6) and Spyogenes 1.9% (0.9-3.3). An intermediary IE prevalence was found with Sanginosus 4.8% (3.0-7.3), Ssalivarius 5.8% (2.9-10.1), and Sagalactiae 9.1% (6.6-12.1). The highest IE prevalence was found with Smitis/oralis 19.4% (15.6-23.5), Sgallolyticus (formerly Sbovis) 30.2% (24.3-36.7), Ssanguinis 34.6% (26.6-43.3), Sgordonii 44.2% (34.0-54.8), and Smutans 47.9% (33.3-62.8). In multivariable analysis using S pneumoniae as reference, all species except S pyogenes were associated with significantly higher IE risk, with the highest risk found with S gallolyticus odds ratio (OR) 31.0 (18.8-51.1), S mitis/oralis OR 31.6 (19.8-50.5), S sanguinis OR 59.1 (32.6-107), S gordonii OR 80.8 (43.9-149), and S mutans OR 81.3 (37.6-176). CONCLUSIONS: The prevalence of IE in streptococcal BSIs is species dependent with S mutans, S gordonii, S sanguinis, S gallolyticus, and S mitis/oralis having the highest IE prevalence and the highest associated IE risk after adjusting for IE risk factors.

All-cause Mortality Due to Bacteremia during a 60-Day Non-Physician Healthcare Worker Strike.

This study explored all-cause mortality of bacteremia diagnosed during a 60-day non-physician healthcare worker strike in 2008. A significant change, with 5.0% (95% confidence interval [CI] 1.2-8.7%, P < .01) absolute risk increase, was seen in 90-day mortality during the strike (n = 598) compared with the rest of the study period 2000-2015 (n = 75 647).

Intravenous mecillinam compared with other ß-lactams as targeted treatment for Escherichia coli or Klebsiella spp. bacteraemia with urinary tract focus.

BACKGROUND: Mecillinam (amdinocillin) is active against Gram-negative bacteria. Clinical data on the efficacy of IV mecillinam for severe urinary tract infections is sparse. OBJECTIVES: To assess the effectiveness of targeted IV mecillinam compared with other ß-lactams for bacteraemia with Escherichia coli and Klebsiella spp. and a urinary tract focus. PATIENTS AND METHODS: We performed a retrospective cohort study at five university hospitals in the Capital Region of Denmark from 1 January 2012 to 31 December 2017. We used Cox proportional hazard regression to compare the primary composite endpoint (all-cause mortality or bacteraemia recurrence within 30 days) between patients treated with mecillinam versus ampicillin, cefuroxime, piperacillin/tazobactam and meropenem. RESULTS: We included 1129 patients in the primary analysis, of which 146 were given IV mecillinam as targeted treatment. We found no significant difference in the primary endpoint between patients treated with mecillinam versus ampicillin and cefuroxime, but found a higher risk for the primary endpoint in the piperacillin/tazobactam and meropenem groups, with adjusted HRs of 2.22 (95% CI 1.24-3.97, P < 0.01) and 2.48 (95% CI 1.04-5.93, P = 0.04), respectively, compared with mecillinam. CONCLUSIONS: The results of this study suggest that IV mecillinam may be a suitable targeted treatment for bacteraemia with a urinary tract focus. However, these results need confirmation by randomized controlled studies.

Proposal for the use of echocardiography in bloodstream infections due to different streptococcal species.

BACKGROUND: Infective endocarditis (IE) is diagnosed in 7-8% of streptococcal bloodstream infections (BSIs), yet it is unclear when to perform transthoracic (TTE) and transoesophageal echocardiography (TOE) according to different streptococcal species. The aim of this sub-study was to propose a flowchart for the use of echocardiography in streptococcal BSIs. METHODS: In a population-based setup, we investigated all patients admitted with streptococcal BSIs and crosslinked data with nationwide registries to identify comorbidities and concomitant hospitalization with IE. Streptococcal species were divided in four groups based on the crude risk of being diagnosed with IE (low-risk < 3%, moderate-risk 3-10%, high-risk 10-30% and very high-risk > 30%). Based on number of positive blood culture (BC) bottles and IE risk factors (prosthetic valve, previous IE, native valve disease, and cardiac device), we further stratified cases according to probability of concomitant IE diagnosis to create a flowchart suggesting TTE plus TOE (IE > 10%), TTE (IE 3-10%), or "wait & see" (IE < 3%). RESULTS: We included 6393 cases with streptococcal BSIs (mean age 68.1 years [SD 16.2], 52.8% men). BSIs with low-risk streptococci (S. pneumoniae, S. pyogenes, S. intermedius) are not initially recommended echocardiography, unless they have ≥3 positive BC bottles and an IE risk factor. Moderate-risk streptococci (S. agalactiae, S. anginosus, S. constellatus, S. dysgalactiae, S. salivarius, S. thermophilus) are guided to "wait & see" strategy if they neither have a risk factor nor ≥3 positive BC bottles, while a TTE is recommended if they have either ≥3 positive BC bottles or a risk factor. Further, a TTE and TOE are recommended if they present with both. High-risk streptococci (S. mitis/oralis, S. parasanguinis, G. adiacens) are directed to a TTE if they neither have a risk factor nor ≥3 positive BC bottles, but to TTE and TOE if they have either ≥3 positive BC bottles or a risk factor. Very high-risk streptococci (S. gordonii, S. gallolyticus, S. mutans, S. sanguinis) are guided directly to TTE and TOE due to a high baseline IE prevalence. CONCLUSION: In addition to the clinical picture, this flowchart based on streptococcal species, number of positive blood culture bottles, and risk factors, can help guide the use of echocardiography in streptococcal bloodstream infections. Since echocardiography results are not available the findings should be confirmed prospectively with the use of systematic echocardiography.

Treatment duration of pivmecillinam in men, non-pregnant and pregnant women for community-acquired urinary tract infections caused by Escherichia coli: a retrospective Danish cohort study.

OBJECTIVES: To evaluate the importance of treatment duration for therapeutic efficacy of pivmecillinam for community-acquired urinary tract infections (UTIs) caused by Escherichia coli. METHODS: A retrospective cohort study was conducted between 1 January 2010 and 30 September 2016 in adults with community-acquired E. coli bacteriuria, treated empirically with pivmecillinam. Regimens of 3, 5 and 7 days were compared using clinical treatment failure (i.e. redemption of a new antibiotic or hospitalization due to UTI) within 14 and 30 days as outcome. HR and risk difference with 95% CI were estimated for treatment failure. Results were stratified by age (18-50, 51-70, >70 years) and sex. RESULTS: Of the 21864 cases of E. coli UTI that were analysed, 2524 (11.5%) were in men. In 954 cases (4.4%) E. coli produced ESBL and 125 (13.1%) of the cases were in men. The 3 day regimen increased the risk of treatment failure for all groups. The risk differences between the 3 and 5 day regimens were <10% for women, but >10% for men. Comparing the 7 day and 5 day regimens, only women aged >50 years demonstrated an increased risk of treatment failure within 14 days with the 5 day regimen, but not within 30 days. CONCLUSIONS: With the current data, where data on clinical classification of the E. coli UTI were missing, a 5 day treatment with pivmecillinam at 400 mg three times daily seems to be the rational recommendation for lower UTI in men, pregnant women and women >50 years old. A 3 day regimen seems sufficient for non-pregnant women <50 years old.

The effect of short-course gentamicin therapy on kidney function in patients with bacteraemia-a retrospective cohort study.

The nephrotoxic potential of aminoglycosides is primarily correlated to the duration of therapy. However, there are discrepancies between previous studies regarding the effect of short course treatment. The aim of this study was to compare renal function, renal recovery and mortality in a large cohort of patients with bacteraemia, who were empirically treated with regimens with and without a short course (≤ 3 days) of once daily dosing of gentamicin. This was a retrospective propensity score-matched cohort study based on all patients with bacteraemia in a Danish hospital in the period 2010-2013. We included 702 patients who received gentamicin, and 702 who did not receive gentamicin. To determine the impact of gentamicin on renal function, we used a modified version of the Kidney Disease: Improving Global Outcomes (KDIGO) criteria for acute kidney injury (AKI), and the resulting data were analyzed by logistic regression. We used Cox regression analysis to compare the adjusted mortality rates between the two groups. According to the KDIGO criteria, we found no significant difference in the occurrence of AKI between the two groups (odds ratio (OR) 0.90 (95% CI 0.68-1.20)). We found that recovery of renal function was similar in the two groups, OR 1.00 (95% CI 0.63-1.60). The hazard ratio for 90-day all-cause mortality was 1.02 (95% CI 0.84-1.25). Short-course empirical gentamicin treatment of patients with bacteraemia was not associated with an increased incidence of AKI nor all-cause mortality in this study, and we observed similar reversibility of renal function.

Impact of antibiotic restriction on resistance levels of Escherichia coli: a controlled interrupted time series study of a hospital-wide antibiotic stewardship programme.

OBJECTIVES: We evaluated the effect of an antibiotic stewardship programme (ASP) on the use of antibiotics and resistance levels of Escherichia coli using a method that allowed direct comparison between an intervention hospital and a control hospital. METHODS: The study was conducted as a retrospective controlled interrupted time series (ITS) at two university teaching hospitals, intervention and control, with 736 and 552 beds, respectively. The study period was between January 2008 and September 2014. We used ITS analysis to determine significant changes in antibiotic use and resistance levels of E. coli. Results were directly compared with data from the control hospital utilizing a subtracted time series (STS). RESULTS: Direct comparison with the control hospital showed that the ASP was associated with a significant change in the level of use of cephalosporins [-151 DDDs/1000 bed-days (95% CI -177, -126)] and fluoroquinolones [-44.5 DDDs/1000 bed-days (95% CI -58.9, -30.1)]. Resistance of E. coli showed a significant change in slope for cefuroxime [-0.13 percentage points/month (95% CI -0.21, -0.057)] and ciprofloxacin [-0.15 percentage points/month (95% CI -0.26, -0.038)]. CONCLUSIONS: The ASP significantly reduced the use of cephalosporins and fluoroquinolones, with concomitant decreasing levels of E. coli resistance to cefuroxime and ciprofloxacin. The same development was not observed at the control hospital.

Parents' socioeconomic factors related to high antibiotic prescribing in primary health care among children aged 0-6 years in the Capital Region of Denmark.

OBJECTIVE: To investigate the distribution of antibiotic prescriptions in primary health care among children aged 0-6 years and its association with socioeconomic factors. DESIGN: A cross-sectional study describing antibiotic prescriptions and socioeconomic factors, using different population-based registers from Statistics Denmark. SETTING: Antibiotic prescriptions in 2012 from primary health care in the Capital Region of Denmark. SUBJECTS: The population of children aged 0-6 years (n = 139,398) in the Capital Region of Denmark. MAIN OUTCOME MEASURES: High use of antibiotics identified by number of antibiotic prescriptions (≥ 3 prescriptions per year) and defined daily doses (DDD). A multinomial logistic regression analysis estimating the association between high antibiotic use and parents' education, employment status, income, child's sex, and ethnic background. RESULTS: Ten percent of children accounted for 25% of the total use DDD. There was a clear tendency that the risk for high antibiotic use increased as parental educational level decreased. The risk for high use was the highest among children of mothers and fathers with basic schooling ≤10 years (OR 1.60, 95% CI 1.29-1.98, and OR 1.60, 95% CI 1.34-1.91, respectively). Low income and unemployment were not associated with high antibiotic use. CONCLUSION: Socioeconomic factors can only partially explain differences in antibiotic use. Further research is needed to clarify the unequal distribution of antibiotic prescribing and the association between high antibiotic use and low educational level. This would provide valuable information in the planning of strategies to promote rational use of antibiotics among children. KEY POINTS The Capital Region of Denmark has the highest rate of antibiotic prescribing in Denmark. Preschool children are among the age groups with the highest use. Ten percent of the children accounted for 25% of the total antibiotic use. Low parental educational level was associated with increased antibiotic use. Parents' income or employment status was not found to be associated with high antibiotic use.

Antibiotic prophylaxis for transrectal prostate biopsy-a new strategy.

BACKGROUND: Fluoroquinolones are extensively used as prophylaxis for transrectal ultrasound-guided biopsy of the prostate (TRUBP). Emerging fluoroquinolone resistance and selection of multiresistant organisms warrant new prophylactic strategies. Pivmecillinam and amoxicillin/clavulanic acid have mutual synergistic activity and the combination of these agents has a broad coverage of the majority of microorganisms causing infectious complications after TRUBP and may be a valuable future prophylactic regimen. PATIENTS AND METHODS: This was a retrospective cohort study of 2624 men that underwent TRUBP at a Danish university hospital. The patients were divided into three groups. Group 1 (n = 1220) received ciprofloxacin before TRUBP, Group 2 (n = 240) received a combination of pivmecillinam and amoxicillin/clavulanic acid before TRUBP and Group 3 (n = 1161) received an extended prophylaxis with pivmecillinam and amoxicillin/clavulanic acid before and for 2 days after TRUBP. RESULTS: One hundred and ten out of 148 (74.3%) post-TRUBP infections were caused by Escherichia coli, Klebsiella pneumoniae or Enterococcus faecalis. Group 3 with the extended prophylaxis with pivmecillinam and amoxicillin/clavulanic acid had a significantly lower rate of bacteraemia (0.9%) as compared with Group 1 (1.8%) and Group 2 (3.7%). A significant fall in the proportion of ESBL-producing Enterobacteriaceae was observed from the period when ciprofloxacin was used as prophylaxis (8.1%) compared with the subsequent period when pivmecillinam and amoxicillin/clavulanic acid was used (5.9%). CONCLUSIONS: The combination of pivmecillinam and amoxicillin/clavulanic acid is an attractive prophylaxis for TRUBP from a clinical, bacteriological and ecological point of view as compared with ciprofloxacin.

Penicillin allergy delabeling has a significant impact on subsequent antibiotic use in primary care.

Efforts to delabel penicillin allergic patients are important as the majority of suspected penicillin allergy can be ruled out by relevant allergy testing. The aim is to change the antibiotic pattern in delabeled patients to minimize use of unnecessary broad-spectrum antibiotics, reducing the risk of antimicrobial resistance and making treatment more cost effective. However, published information on subsequent antibiotic use is scarce. To evaluate the effect of delabeling on subsequent antibiotic use in primary care, a cohort of 2911 patients tested for penicillin allergy was compared to a matched control group of 14,522 individuals from the background population. In total 86.4% of the tested patients were delabeled. For delabeled patients, penicillin use increased from 0.07 prescriptions per patient year before allergy investigation, to 0.53 prescriptions per patient year post investigation (p < 0.001). The use of fluoroquinolones and macrolides was reduced and reached a level comparable to the background population. This study shows that penicillin allergy delabeling has significant positive impact on subsequent antibiotic use in primary care, and that penicillin use increases to levels similar to the background population. Penicillin allergy delabeling should be prioritized as an important and efficient element in antimicrobial stewardship initiatives.