Infections are among the most common acute complications after stroke and associated with poor outcome (1, 2). Prophylactic antimicrobial treatment effectively reduced infection rates in experimental models of stroke (3) and clinical proof-of-concept studies [for a meta-analysis, see the study by Westendorp et al. (4)]. However, the impact of preventive antibiotic treatment on long-term functional outcome remained unclear, as previous clinical trials were not sufficiently powered to address this issue. Recently, two large randomized controlled phase III clinical trials demonstrated that antibiotics commonly used to treat stroke-associated pneumonia (SAP) neither reduce the frequency of pneumonia nor improve the outcome after stroke when administered in a prophylactic manner (5–7).

Current European and US stroke guidelines strictly recommend early antibiotic treatment of poststroke infections but advise against their prophylactic use (8). Biomarkers might help to identify patients in the early subclinical course of SAP or even at high risk for developing SAP, thereby tailoring antibiotic treatment to patients with the highest probability to benefit while reducing the risk of antibiotic resistances (9). Procalcitonin (PCT), an early marker of severe bacterial infections (10), has been useful in diagnosing SAP in previous observational clinical studies (11, 12). In addition, PCT guidance has been shown to reduce the duration of antibiotic treatment in critically ill patients, without compromising patients’ safety. In this study, we investigated whether PCT ultrasensitive (PCTus)-guided antibiotic treatment improves functional outcome after severe stroke by early identification and treatment of pneumonia.

Between February 2011 and April 2014, 235 patients were enrolled and randomly assigned to the 2 study groups. Eight patients withdrew consent after study enrollment but before the first study-related assessment was performed, resulting in a total of 227 patients for the ITT analysis (112 in the PCT group and 115 in the control group). Two hundred six patients (104 in the PCT group and 102 in the control group) were included in the PP analysis. Adherence to PCT guidance was 65%, leaving 170 patients for the PP^adherence analysis (68 in the PCT group and 102 in the control group). Physicians overruled PCT guidance either by treating with antibiotics despite PCT values below the cutoff (28% of patients in the PCT group) or by not treating patients with antibiotics although PCT values were above the cutoff value indicative of an underlying bacterial infection (37% of patients in the PCT group). Eight centers included more than 10 patients into this study. Among these, the adherence to PCT guidance ranged between 33 and 100% (mean 60%). The 3-month follow-up was completed by 197 (87%) patients from ITT group. The rate of 3-month follow-ups was 84% (n = 97) in the control group and 89% (n = 100) in the PCT group (Figure 1; p = 0.28).

The study groups did not differ regarding baseline demographic and clinical characteristics, except for a higher rate of chronic obstructive pulmonary disease (COPD) in the PCT group and a higher rate of diabetes mellitus in the control group (Table 1). There was a trend toward higher baseline mRS scores at the time of the initial study visit in the control group (p = 0.067 in ITT; p = 0.070 in PP).

Apart from SAP, the frequency of SAEs was low. There was no significant difference in the frequency of SAEs between the study groups (Table 2).

Procalcitonin-based antibiotic therapy guidance was not associated with an increased proportion of acceptable outcome (mRS ≤ 4) at 3 months, neither in the ITT (OR 0.79, 95% CI 0.45–1.39, p = 0.47) nor in the PP (OR 0.71, 95% CI 0.39–1.48, p = 0.29) or PP^adherence analyses (OR 0.81, 95% CI 0.42–1.57, p = 0.61, Table 3). The mRS distribution 3 months after stroke onset in both study groups is shown in Figure 2. In secondary endpoint analyses, outcome at 6 months was similar between both groups (p = 0.66 for ITT population). A shift analysis of the mRS (15) also revealed no significant differences between the groups. In all shift analysis scenarios considered, the proportion of better outcome was lower than the proportion of worse outcome for patients of the PCT group when compared with patients of the control group (Table 4). The proportion of a BI of ≥60 in the 3-month follow-up as a measure for favorable outcome was similar in the PCT and control groups (median BI, ITT: 62.5 in PCT group vs. 55 in control group, p = 0.415; PP: 62.5 in PCT group vs. 55 in control group, p = 0.542). Mortality rates (Figure 3) were not significantly different between groups during 3 months (PCT group vs. control group—ITT: OR 1.20, 95% CI 0.65–2.24; PP: OR 1.28, 95% CI 0.64–2.58) and 6 months of follow-up (PCT vs. control group—ITT: OR 1.34, 95% CI 0.75–2.41; PP: OR 1.42, 95% CI 0.75–2.6).

Within the first week after stroke onset, the presence of SAP or sepsis (with or without further infections) was diagnosed in 64 (28%) patients. Urinary tract infection (UTI) without SAP was diagnosed in 19 (8%) patients. Infection rates within the first 7 days after stroke onset were similar in both study groups (SAP 29% in PCT group vs. 27% in STD group; UTI 7% in PCT group vs. 10% in STD group; Table 5).The median number of days with fever tended to be higher in controls (2 days in control group vs. 1 day in PCT group, p = 0.055; Figure 4A).

In the ITT analysis, antibiotic treatment was more frequent in the PCT compared to the standard group. Sixty-three percent of patients in the PCT group received antibiotic treatment, compared to 45% of patients in the control group (Table 5). The total number of days treated with (any) antibiotics within the first week after stroke onset was 362 [median 3, interquartile range (IQR) 0–6] in the PCT group (n = 112) compared to 250 (median 0, IQR 0–5) in the control group (n = 115) (p = 0.004; Figure 4B). A post hoc analysis of the use of antibiotic substances between day 1 and day 7 after stroke onset showed significant differences between the study groups (Table 6; p = 0.0004).

In contrast to patients with UTIs, SAP patients have a mortality rate that was twice as high as in patients without SAP within 3 months of follow-up (Table 7; p = 0.0055). Pneumonia rates following the acute course of stroke (3-month follow-up: 6% PCT vs. 7% STD, 6-months follow-up: 8% PCT vs. 9% STD) and rehospitalization rates (3-month follow-up: 10% PCT vs. 7% STD, 6-months follow-up: 14% PCT vs. 10% STD) were comparable in both groups.

A post hoc analysis of all PCT values in the ITT population demonstrated a significant increase on the first day of infection in patients with pneumonia and sepsis compared to patients with UTIs or without infections [median (IQR): no infection 0.042 (0.026–0.068), UTI only 0.044 (0.029–0.072), and pneumonia/sepsis 0.076 (0.043–0.175); Figure 5A]. PCT values were significantly higher in patients with SAP or sepsis (±UTI) between day 1 and 7 following stroke onset compared to patients without infections (Figure 5B).

PCT ultrasensitive-guided antibiotic treatment of bacterial pneumonia in acute stroke patients is a safe treatment strategy. However, our study failed to demonstrate an improvement of stroke outcome for this treatment approach. Moreover, SAP and mortality rates were similar in both study groups.

Only recently, two large randomized controlled phase III trials demonstrated neither an improvement of stroke outcome nor a significant reduction of SAP rate by preventive antibiotic therapy (5, 6). Both trials reported a significant reduction in UTIs, which are known to be unrelated to poststroke outcome (7).

In our study, PCTus guidance did not affect the frequency of clinical diagnosis of SAP, since infection rates were similar in both treatment groups. However, the usage of antibiotics (measured in days with antibiotic treatment) was higher in the PCT compared to the control group. Days with fever tended to be reduced by PCTus-guided treatment, which is important to note, since fever is a negative prognostic factor for stroke outcome (16).

Procalcitonin testing has also been shown to improve diagnostic accuracy for SAP in previous observational studies, where it was shown to improve specificity in case of clinical suspicion of SAP (12). Accordingly, a post hoc analysis of PCT values in our study demonstrated a significant increase of PCT in patients with SAP and sepsis on the first day of infection, compared to patients with UTIs or without infections. Although there is a frequent request for biomarkers as a criterion for diagnosing SAP (9, 17), the adherence to the PCT guidance was surprisingly low. In the PCT group, overruling of the PCT guidance by the treating physician was allowed due to ethical concerns. Strict guidance to PCT was followed in only 65% of the patients, with considerable differences between the centers. This may be considered a problem of trust by some physicians in this new treatment approach under testing and may have impacted to some degree the trial outcome.

In clinical routine, physicians diagnose SAP based on clinical criteria, mainly fever, and are influenced by risk factors for SAP, e.g., stroke severity, while biomarkers are only used as additional diagnostic information (17). Overall, clinicians tend to overdiagnose SAP (7), reinforcing the need for operational diagnostic SAP criteria (18, 19). Although robust data are missing, it appears likely that overdiagnosing might cause an overtreatment of patients after stroke. In our trial, patients in the control group were treated according to the current standards of therapy, where management of infections is based on the clinical judgment of the treating physicians. Current European and US stroke guidelines strictly recommend early antibiotic treatment of poststroke infections but advise against their prophylactic use (8). However, while 36% of patients in PCT group and 37% of patients in control group were diagnosed with a poststroke infection, 63% of patients in the PCT group received antibiotic treatment, compared to 45% in the standard group. With a low threshold for antibiotic treatment after stroke in clinical routine, preventive treatment strategies might not be able to add benefits to patients’ care.

The occurrence of SAP was associated with a twofold increase of mortality within 3 months of follow-up, which is in line with previous studies (20). As there is no evidence of improved outcome by preventing infections so far, there is an ongoing discussion whether a causal relationship between SAP and outcome after stroke exists (5, 21). Caution should be exercised not to label SAP as mere marker of detrimental outcome prematurely, as data available so far do not allow excluding a causal relationship. Although patients in both PASS and STROKE-INF received antibiotics that are commonly used for pneumonia treatment in a prophylactic manner, the incidence of SAP remained unchanged compared to patients treated with standard stroke unit care only. This might be due to late initiation of prophylactic treatment in these trials or inappropriate choice of antibiotics (17); however, SAP might also harbor a greater non-infective inflammatory component than previously thought, which might not be prevented by antibiotic treatment alone (7). As a stroke-induced immunosuppressed state is an important risk factor for SAP, the use of targeted immune modulators might be a promising new treatment approach (22).

Our study has several limitations. Our study has small baseline imbalances for stroke severity in favor of the control and for COPD in favor of the PCT group. More importantly, the low adherence to the PCT guidance might have caused an underestimation of the effects of PCTus-guided antibiotic treatment. In addition, the number of included patients was rather small in comparison with the recent phase III studies on preventive antibiotics. However, we only included severely affected stroke patients who are known to have a higher risk of infections, and the overall infection rate in our trial was 37%, which is higher than in the previously reported trials (5, 6). In addition, variations in antibiotic substances and doses might have influenced our results. The high rate of antibiotic treatment in the control group might have confounded benefits of PCTus-guided antibiotic treatment.

In conclusion, our results do not support the use of PCTus-guided antibiotic treatment of SAP to improve long-term outcome after stroke. However, a post hoc analysis of our data affirms that PCTus is a useful biomarker for diagnosis of SAP. The utility of PCTus as a biomarker for the diagnostic setup of SAP needs to be addressed in further trials, e.g., a cutoff level with high positive and negative predictive values needs to be established. Moreover, subsequent trials identifying biomarker patterns for prediction of SAP at stroke onset [among others PCTus, copeptin (23)] might provide the rational basis for biomarker-guided anti-infective immunomodulatory treatment already starting in the hyperacute phase of stroke in patients at risk for SAP.

Benjamin Hotter (site investigator), Department of Neurology, Charité – Universitaetsmedizin Berlin (Campus Benjamin Franklin, Campus Charité Mitte, Campus Virchow-Klinikum), Germany; Center for Stroke Research Berlin Trial Team (site investigator), Department of Neurology, Charité – Universitaetsmedizin Berlin (Campus Benjamin Franklin, Campus Charité Mitte, Campus Virchow-Klinikum), Germany; Daniel Peters (site investigator), Department of Neurology, Unfallkrankenhaus Berlin, Germany; Daniela Thiem-Martin (site investigator), Department of Neurology, Vivantes Klinikum Spandau, Berlin, Germany; Duc Thuan Nguyen (site investigator), Department of Neurology, Vivantes Auguste-Viktoria-Klinikum, Berlin, Germany; Georg Walter (site investigator), Department of Neurology, Vivantes Klinikum Spandau, Berlin, Germany; Grit Lehmann (site investigator), Department of Neurology, Unfallkrankenhaus Berlin, Germany; Jens Offermann (site investigator), Department of Neurology, Vivantes Klinikum Neukoelln, Berlin, Germany; Jos Goehler, Department of Neurology, Charité – Universitaetsmedizin Berlin (Campus Benjamin Franklin, Campus Charité Mitte, Campus Virchow-Klinikum), Germany (site investigator); Olaf Crome, Department of Neurology, Vivantes Klinikum Neukoelln, Berlin, Germany (site investigator); Paul Sparenberg, Department of Neurology, Unfallkrankenhaus Berlin, Germany (site investigator); Sebastian Boettcher, Department of Neurology, Unfallkrankenhaus Berlin, Germany (site investigator); Stephan Kinze, Department of Neurology, Unfallkrankenhaus Berlin, Germany (site investigator); Neurovascular Research Laboratory, Institut de Recerca, Hospital Universitari Vall d’Hebrón, Universitat Autònoma de Barcelona, Spain; Department of Neurology, Universitaetsspital Zuerich, Switzerland; Department of Neurology, Klinikum Frankfurt Oder, Germany.

This study was carried out in accordance with the recommendations of the responsible local ethics committees [the ethics committee of the Charité University Berlin (EA1/267/10) for study centers located in Berlin, the ethics committee of the State Medical Association of Brandenburg (AS 30(a)/2011) for the study center located in Brandenburg, the Kantonale Ethikkommission Zuerich (2013-0195) for the study center in Zuerich, and the Hospital Vall d’Hebron Clinical Research Ethics Committee (TFS-ANT-2012-01) for the study center in Barcelona] with written informed consent from all subjects or their legal representatives. All patients or their legal representatives gave written informed consent in accordance with the Declaration of Helsinki.

LU: design and conceptualization of the study, acquisition of data, analysis and interpretation of data, drafting of manuscript, final approval of the manuscript to be published, and agreement to be accountable for all aspects of the work. SH, DN, MH, B-MM, FH, IS, G-JJ, JM, AB, MK, and AH: acquisition of data, revision of manuscript for intellectual content, final approval of the manuscript to be published, and agreement to be accountable for all aspects of the work. SE and CD: conceptualization of the study, revision of manuscript for intellectual content, final approval of the manuscript to be published, and agreement to be accountable for all aspects of the work. JW and SH: analysis and interpretation of data, revision of manuscript for intellectual content, final approval of the manuscript to be published, and agreement to be accountable for all aspects of the work. CM and SA: design and conceptualization of the study, revision of manuscript for intellectual content, final approval of the manuscript to be published, and agreement to be accountable for all aspects of the work. AM: design and conceptualization of the study, analysis and interpretation of data, drafting of manuscript, final approval of the manuscript to be published, and agreement to be accountable for all aspects of the work.

SA has received honoraria for consultancies from BRAHMS GmbH. Thermo Fisher Scientific provided procalcitonin kits at reduced costs. Thermo Fisher Scientific had no involvement in data collection or patient recruitment. All other authors declare no competing interests.