Introduction
Sepsis is a prevalent disorder and one of the main causes of death among hospitalized patients. Treating sepsis is associated with high costs; however, despite advances in medical practice, the mortality rate of sepsis has not declined in recent decades [
1]. In Spain, the incidence of severe sepsis is 104 cases per 100,000 adult residents per year, and related in-hospital mortality is 20.7%; the incidence of septic shock is 31 cases per 100,000 adult residents per year, and related in-hospital mortality is 45.7% [
2]. Sepsis present at intensive care unit (ICU) admission and ICU-acquired sepsis clearly differ in the types of patients affected, the sources of infection, the microorganisms responsible, and the prognosis [
3].
Diverse studies have confirmed that the prompt institution of antimicrobial therapy active against the causative pathogen is lifesaving in patients with severe sepsis [
4,
5]. The Surviving Sepsis Campaign strongly recommends initiating antibiotic therapy within the first hour of recognition of severe sepsis, after suitable samples have been obtained for cultures [
6].
Nevertheless, although antibiotic therapy is the cornerstone in the treatment of sepsis, the optimal antimicrobial strategy has not been defined. Few data are available about antibiotic prescription patterns used most in severe sepsis.
Furthermore, the advantages and disadvantages of combination therapy compared with monotherapy are controversial, and studies comparing the two approaches have mainly been limited to bacteremia, pneumonia, or serious
Pseudomonas aeruginosa infections [
7‐
9]. Importantly, a recent retrospective study concluded that certain combinations of antimicrobials, including antimicrobials with different targets, improve survival in patients with septic shock [
10].
We present a secondary analysis of the Edusepsis study, which enrolled all patients with severe sepsis and septic shock admitted to the participating ICUs during 2 months in 2005 and 4 months in 2006. Our aims are (a) to describe the patterns of empiric antimicrobial therapy, analyzing the differences between community-acquired and nosocomial infections; and (b) to compare the impact on mortality of combination therapy, including at least two antimicrobials with different mechanisms of action, with that of monotherapy and other combinations of antimicrobials.
Materials and methods
Design of the study
We conducted a secondary analysis of the Edusepsis study, a Spanish national multicenter before-and-after study involving 77 ICUs [
11]. In this study, carried out between November 2005 and 2007, data were collected before and after a 2-month educational intervention based on the Surviving Sepsis Campaign guidelines; this approach to improving treatment of severe sepsis is cost-effective [
12]. Each participating centers' research and ethical-review boards approved the study, and patients remained anonymous. The need for informed consent was waived in view of the observational and anonymous nature of the study.
The study included all patients in these ICUs with severe sepsis or septic shock. The study design is described in detail elsewhere [
11]. In brief, severe sepsis was defined as sepsis associated with organ dysfunction unexplained by other causes. Septic shock was defined as sepsis associated with systolic blood pressure <90 mm Hg, mean arterial pressure <65 mm Hg, or a reduction in systolic blood pressure >40 mm Hg from baseline despite adequate volume resuscitation. Patients in whom the onset of severe sepsis could not be determined were excluded from the analysis. The approach to data collection and the quality-control measures to assure data reliability also are described elsewhere [
11,
12].
Variables
The following variables were recorded: demographic characteristics (age and gender), types of patients (medical, trauma, emergency surgery, elective surgery), sources of infection, location at sepsis acquisition (community-acquired or nosocomial infection), and baseline lactate level and organ dysfunction at sepsis diagnosis. Severity of illness was evaluated by the Acute Physiology and Chronic Health Evaluation (APACHE) II score, considering the worst reading in the first 24 hours in the ICU [
13]. All patients were followed up until death or hospital discharge. The primary outcome variable was in-hospital mortality.
Antimicrobial therapy
The antimicrobial therapy prescribed at the diagnosis of severe sepsis and the time from severe sepsis presentation to antibiotic administration were recorded. To facilitate subsequent analysis, antimicrobial agents were grouped into eight antibiotic families: β-lactams (except carbapenems), carbapenems, quinolones, macrolides, aminoglycosides, anti-gram-positive antibiotics (vancomycin, teicoplanin, and linezolid), antifungal agents, and other antimicrobial agents (including antiviral and tuberculostatic agents). Data for community-acquired and nosocomial infections also were analyzed separately. We also compared the clinical characteristics of patients that received different-class combination therapy (DCCT) with those of patients that received any other antimicrobial therapy (non-DCCT).
DCCT was defined as the concomitant use of two or more antibiotics of different mechanistic classes, as recently defined by Kumar
et al. [
10], specifically β-lactams or carbapenems with aminoglycosides, fluoroquinolones, or macrolides/clindamycin. Monotherapy or any other combination therapy was considered non-DCCT for this analysis.
To assess the impact of DCCT on mortality, we analyzed only patients who received the first dose of antimicrobial within the first 6 hours after severe sepsis presentation.
Statistical analysis
Discrete variables were expressed as frequencies (percentage), and continuous variables, as means and standard deviations (SDs), unless stated otherwise; all statistical tests were two-sided. Differences in categoric variables were calculated by using χ2 tests or Fisher Exact test, and differences in continuous variables were calculated by using the Mann-Whitney U or Kruskal-Wallis test, as appropriate.
Backward logistic regression was used to assess the factors independently associated with in-hospital mortality. To avoid spurious associations, variables entered in the regression models were those with a relation in univariate analysis (P ≤ 0.05) or a plausible relation with the dependent variable. SPSS for Windows 20.0 (SPSS, Chicago, IL, USA) was used for all statistical analyses.
Discussion
This secondary analysis of the Edusepsis study reveals interesting data about the patterns of antibiotic prescription in patients with severe sepsis and septic shock and about the characteristics of patients receiving combination therapy, including antimicrobials, with different mechanisms of action (DCCTs) versus those receiving either monotherapy or any other combinations of antimicrobials (non-DCCTs). Our study confirms the increased survival in patients administered DCCTs (β-lactams plus aminoglycosides, quinolones, or macrolides/clindamycin) within the first 6 hours of severe sepsis presentation. We excluded patients that received antimicrobial therapy after 6 hours of severe sepsis diagnosis from this analysis, because strong evidence indicates that early administration increases survival in patients with severe sepsis or septic shock [
4,
5,
10].
Appropriate empiric antimicrobial therapy is crucial for the survival of sepsis patients [
4,
5]. Formerly, multidrug-resistant pathogens were found almost exclusively in nosocomial infections. However, community-acquired infections are now often caused by antibiotic-resistant bacteria (for example, extended-spectrum β-lactamase-producing Enterobacteriaceae, multidrug-resistant
Pseudomonas aeruginosa, or methicillin-resistant
Staphylococcus aureus) [
14,
15]. This striking change in epidemiology may explain why the initial therapy frequently includes a combination of different antimicrobial agents [
16].
β-Lactams, including carbapenems, are the most commonly used antibiotics in the critical care setting [
17]. Likewise, this antibiotic family constitutes the mainstay of empiric treatment in patients with severe sepsis or septic shock, whether administered alone or in combination with other antimicrobials. Carbapenems are more frequently prescribed in patients with nosocomial sepsis, although it is worth mentioning that one in five patients with community-acquired sepsis is treated empirically with a carbapenem. This may reflect the increase in multidrug-resistant gram-negative pathogens in the community [
14]. Carbapenems might have been analyzed in conjunction with the rest of β-lactams. However, we decided to analyze them separately from other β-lactams because of the broader-spectrum, major role in empiric antibiotic therapy and the widespread use in the ICU.
Quinolones are used mainly in community-acquired infections and in combination therapy [
18]. The extended use of quinolones in combination therapy in patients with severe community-acquired pneumonia may explain the increasing rate of quinolone resistance among nosocomial gram-negative pathogens [
18,
19].
Numerous studies have evaluated the likely superiority of combination therapy in patients with diverse types of infections. A French multicenter study of critical patients with acute peritonitis found no difference in the rate of therapeutic failure or length of antibiotic treatment when β-lactams were administered alone or in combination with aminoglycosides, concluding that aminoglycosides should be added only when an infection by
Pseudomonas spp or
Enterococcus spp is suspected [
20]. Two randomized clinical trials found no benefits of combination therapy over monotherapy in patients with ventilator-associated pneumonia [
21,
22]. Moreover, in one trial, monotherapy was associated with lower rates of therapeutic failure, superinfection, and side effects [
22].
Conversely, diverse studies have demonstrated lower mortality and length of stay in patients with pneumococcal bacteremia or with community-acquired pneumonia receiving combination therapy, including a β-lactam plus a macrolide or a quinolone, than in those receiving monotherapy [
23‐
25]. In these studies, the benefits seem to be restricted to more-severe patients or to those in septic shock [
18,
23]. Conversely, a recent retrospective study concluded that, in bacteremia caused by gram-negative bacilli, combination therapy with β-lactams and fluoroquinolones was associated with a reduction in 28-day crude mortality only among less severely ill patients [
7].
Two meta-analyses of studies performed in patients with gram-negative bacteremia or sepsis found no benefit of combination therapy over monotherapy, except when bacteremia was caused by multidrug-resistant bacteria or
Pseudomonas spp [
26,
27]. Moreover, higher rates of side effects (mainly nephrotoxicity) were reported in the group of patients treated with β-lactam antibiotics plus aminoglycosides. More recently, a meta-analytic/meta-regression study that included 50 studies found that combination antibiotic therapy improves survival, particularly in septic shock patients, but may be harmful to less severely ill patients [
28].
Nevertheless, few data are available about the impact on the outcome of combination therapy in large cohorts of patients with severe sepsis or septic shock. A recent propensity-matched analysis concluded that, in patients with septic shock, the use of combination therapy with two or more antibiotics of different mechanistic classes was associated with lower 28-day mortality, shorter ICU stay, and lower in-hospital mortality [
10].
Our results confirm that combination therapy, including two or more antimicrobials with different mechanisms of action (β-lactams in combination with aminoglycosides, fluoroquinolones, or macrolides/clindamycin), administered within the first 6 hours of sepsis presentation is an independent protective factor against in-hospital mortality. Interestingly, severity of illness measured by APACHE II score, basal lactate levels, and the presence of hemodynamic failure did not differ between patients receiving DCCTs and those receiving non-DCCTs.
The choice of empiric antimicrobial therapy is based on the clinical presentation of the infection, the characteristics of the patient, the local ecology, and previous antibiotic exposure. Reducing the antibiotic pressure and side effects are the main reasons for choosing monotherapy. Conversely, the main reason for prescribing combination therapy for critically ill sepsis patient is to broaden the antimicrobial spectrum in an attempt to ensure the coverage of all likely pathogens. Our results permit us to speculate that the synergistic mechanisms of different antimicrobial combinations, or the immunomodulatory effects described with macrolides and quinolones, may be of clinical transcendence in patients with severe sepsis or septic shock [
29‐
31].
Our study has several limitations. First, a major limitation in our study is the lack of microbiology data due to the initial study design. Accordingly, no data are available on antibiotic susceptibility, appropriateness of antimicrobial therapy, or the presence of bacteremia. Appropriate antimicrobial therapy based on culture results was an important determinant of survival in a large cohort of patients with severe sepsis [
32].
Second, because of the absence of microbiology data, we cannot explore whether the positive impact on mortality observed with DCCTs is related to a synergistic effect of two mechanistically distinct antibiotics or a broader range of coverage with two or more agents.
Third, we did not evaluate source control and other important measures included in the Surviving Sepsis Campaign care bundles.
Fourth, this is a secondary analysis of an observational study. Nevertheless, properly designed observational studies with the appropriate analytic approach can provide valuable information on treatment effectiveness [
4].
However, our study has also important strengths. We prospectively enrolled a large cohort of ICU patients with severe sepsis and septic shock in a short time and monitored them until death or hospital discharge, resulting in a homogeneous database with high quality-control measures that assure data validity [
4]. Finally, our conclusions are strengthened by absence of immortal bias.
Acknowledgements
We received statistical support from David Suarez, MSc from Unidad de Epidemiologia, Fundación Parc Tauli, Universidad Autónoma de Barcelona. Barcelona, Spain; and data monitoring from Gemma Gomà, research nurse from Centro de Críticos, Hospital de Sabadell. Sabadell, Spain.
The Edusepsis Study Group included Ana Navas, Ricard Ferrer, Antonio Artigas (Hospital de Sabadell, Consorci Hospitalari Parc Tauli); María Álvarez (Hospital de Terrassa); Josep Maria Sirvent, Sara Herranz Ulldemolins (Hospital Universitari Josep Trueta de Girona); Pedro Galdós, Goiatz Balziscueta (Hospital General de Móstoles); Pilar Marco, Izaskun Azkarate (Hospital de Donostia); Rafael Sierra (Hospital Universitario Puerta del Mar); José Javier Izua (Hospital Virgen del Camino); José Castaño (Hospital Universitario Virgen de las Nieves); Alfonso Ambrós, Julian Ortega (Hospital General de Ciudad Real); Virgilio Corcoles (Complejo Hospitalario Universitario de Albacete); Luis Tamayo (Hospital Río Carrión); Demetrio Carriedo, Milagros Llorente (Hospital de León); Paz Merino, Elena Bustamante (Hospital Can Misses); Eduardo Palencia, Pablo García Olivares, Patricia Santa Teresa Zamarro (Hospital Gregorio Marañon Madrid); Carlos Pérez (Hospital Santiago Apóstol); Ana Renedo (Hospital Morales Messeguer); Silvestre Nicolás-Franco (Hospital Rafael Méndez); María Salomé Sánchez (Hospital Vega Baja); Francisco Javier Gil (Hospital Santa Maria del Rosell); María Jesús Gómez (Hospital General Universitario Reina Sofía de Murcia); Enrique Piacentini (Hospital Mútua de Terrassa); Ana Loza (Hospital Universitario de Valme); Jordi Ibáñez (Hospital Son Dureta); Silvia Rodríguez (Hospital de Manresa); Jose Ángel Berezo, Jesús Blanco (Hospital Río Hortega Valladolid); Angeles Gabán, Mª Jesús López Cambra, Alec Tallet (Hospital General de Segovia); Miguel Martínez, Jose Antonio Fernández, Fernando Callejo, Mª Jesús López Pueyo (Hospital General Yagüe); Francisco Gandía (Hospital Clínico Universitario de Valladolid); Mª José Fernández (Hospital Santa Bárbara); Juan Carlos Ballesteros (Hospital Universitario de Salamanca); María Teresa Antuña, Santiago Herrero (Hospital de Cabueñes); Manuel Valledor, Mª Jose Gutierrez (Hospital San Agustín); Carmen Pérez (Hospital Universitario Insular Gran Canaria); Oscar Rodríguez (Hospital Clínico Universitario de Valencia); Rafael Dominguez (Hospital Alto Guadalquivir); Josefa Peinado (Empresa Pública Hospital de Poniente); María Victoria de la Torre, Cristina Salazar (Hospital Virgen Victoria de Málaga); Mª Cruz Martín, Joaquin Ramon (Centro Médico Delfos); Fernando Iglesias Llaca, Lorena Forcelledo Espina, Francisco Taboada Costa, José Antonio Gonzalo Guerra (Hospital Universitario Central de Asturias); Francisco José Guerrero, Felipe Cañada, Mª Milagros Balaguer, Isabel Mertín, Carmen López, Daniel Sánchez (Hospital Torrecardenas); Josep Costa, Calizaya (Hospital de Barcelona SCIAS); Angel Arenaza, Ana Mª Morillo, Daniel Del Toro, Tomás Guzman (Hospital Virgen de la Macarena); Antonio Blesa, Fernando Martínez, Alejandro Moneo (Hospital San Carlos); Mª Jesús Broch (Hospital de Sagunt); Jose Antonio Camacho (Hospital San Agustín de Linares); Francisco J. Garcia (Hospital de Montilla); Xosé Luis Pérez (Hospital Universitario de Bellvitge); Nieves Garcia (Hospital Universitario La Princesa); Juan Carlos Ruiz, Jesús Caballero, Esther Francisco, Tania Requena, Adolfo Ruiz, José Luis Bóveda (Hospital Universitari Vall Hebrón); José Miguel Soto, Constantino Tormo (Hospital Universitario Dr Peset); Rafael Blancas (Hospital La Mancha-Centro); Manuel Quintana, Miguel Ángel Taberna (Hospital Nuestra Sra del Prado); Jose Maria Añon, Juan B. Aranjo (Hospital Virgen de la Luz); Manuel Rodríguez (Hospital Juan Ramon Jiménez); José Maria Garcia (Hospital La Serrania de Ronda); Mª Isabel Rodríguez (Hospital General de Baza); Mª Jesús Huertos (Hospital Universitario Puerto Real); Carlos Ortiz (Hospital Virgen del Rocio); Mª Eugenia Yuste (Hospital Universitario San Cecilio); Juan Francisco Machado (Hospital Santa Ana-Motril); Dolores Ocaña (Hospital La Inmaculada); Ramón Vegas (Hospital Valle de los Pedroches); and Luis Vallejo (Hospital SAS La Linea).
Competing interests
The authors declare that they have no competing interests.
Authors' contributions
As principal investigator, ADM had full access to all data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis. Study concept and design were performed by ADM, MLMG, RF, AA, JGM. RF completed the acquisition of data. Analysis and interpretation of data were performed by ADM and RF. Drafting of the manuscript was executed by ADM and JGM. Critical revision of the manuscript for important intellectual content was done by MLMG, COL, EP, MJLP, IML, ML, and AA. RF and AA carried out the Edusepsis General Coordination and Surviving Sepsis Campaign coordination by ML. All authors critically revised and approved the manuscript.