Efficacy of Early Oral Switch with β-Lactams for Low-Risk Staphylococcus aureus Bacteremia

Early Oral Antibiotic Switch in Staphylococcus aureus Bacteraemia: The Staphylococcus aureus Network Adaptive Platform (SNAP) Trial Early Oral Switch Protocol

BACKGROUND

Staphylococcus aureus bloodstream infection (bacteremia) is traditionally treated with at least 2 weeks of intravenous (IV) antibiotics in adults, 3-7 days in children, and often longer for those with complicated disease. The current practice of treating S. aureus bacteremia (SAB) with prolonged IV antibiotics (rather than oral antibiotics) is based on historical observational research and expert opinion. Prolonged IV antibiotic therapy has significant disadvantages for patients and healthcare systems, and there is growing interest in whether a switch to oral antibiotics following an initial period of IV therapy is a safe alternative for clinically stable patients.

PROTOCOL

The early oral switch (EOS) domain of the S. aureus Network Adaptive Platform (SNAP) trial will assess early switch to oral antibiotics compared with continued IV treatment in clinically stable patients with SAB. The primary endpoint is 90-day all-cause mortality. Hospitalised SAB patients are assessed at platform day 7 ±2 (uncomplicated SAB) and day 14 ±2 (complicated SAB) to determine their eligibility for randomization to EOS (intervention) or continued IV treatment (current standard of care).

DISCUSSION

Recruitment is occurring in the EOS domain of the SNAP trial. As of August 2023, 21% of all SNAP participants had been randomized to the EOS domain, a total of 264 participants across 77 centers, with an aim to recruit at least 1000 participants. We describe challenges and facilitators to enrolment in this domain to aid those planning similar trials.

Efficacy and safety of an early oral switch in low-risk Staphylococcus aureus bloodstream infection (SABATO): an international, open-label, parallel-group, randomised, controlled, non-inferiority trial

BACKGROUND

Staphylococcus aureus bloodstream infection is treated with at least 14 days of intravenous antimicrobials. We assessed the efficacy and safety of an early switch to oral therapy in patients at low risk for complications related to S aureus bloodstream infection.

METHODS

In this international, open-label, randomised, controlled, non-inferiority trial done in 31 tertiary care hospitals in Germany, France, the Netherlands, and Spain, adult patients with low-risk S aureus bloodstream infection were randomly assigned after 5-7 days of intravenous antimicrobial therapy to oral antimicrobial therapy or to continue intravenous standard therapy. Randomisation was done via a central web-based system, using permuted blocks of varying length, and stratified by study centre. The main exclusion criteria were signs and symptoms of complicated S aureus bloodstream infection, non-removable foreign devices, and severe comorbidity. The composite primary endpoint was the occurrence of any complication related to S aureus bloodstream infection (relapsing S aureus bloodstream infection, deep-seated infection, and mortality attributable to infection) within 90 days, assessed in the intention-to-treat population by clinical assessors who were masked to treatment assignment. Adverse events were assessed in all participants who received at least one dose of study medication (safety population). Due to slow recruitment, the scientific advisory committee decided on Jan 15, 2018, to stop the trial after 215 participants were randomly assigned (planned sample size was 430 participants) and to convert the planned interim analysis into the final analysis. The decision was taken without knowledge of outcome data, at a time when 126 participants were enrolled. The new sample size accommodated a non-inferiority margin of 10%; to claim non-inferiority, the upper bound of the 95% CI for the treatment difference (stratified by centre) had to be below 10 percentage points. The trial is closed to recruitment and is registered with ClinicalTrials.gov (NCT01792804), the German Clinical trials register (DRKS00004741), and EudraCT (2013-000577-77).

FINDINGS

Of 5063 patients with S aureus bloodstream infection assessed for eligibility, 213 were randomly assigned to switch to oral therapy (n=108) or to continue intravenous therapy (n=105). Mean age was 63·5 (SD 17·2) years and 148 (69%) participants were male and 65 (31%) were female. In the oral switch group, 14 (13%) participants met the primary endpoint versus 13 (12%) in the intravenous group, with a treatment difference of 0·7 percentage points (95% CI -7·8 to 9·1; p=0·013). In the oral switch group, 36 (34%) of 107 participants in the safety population had at least one serious adverse event compared with 27 (26%) of 103 participants in the intravenous group (p=0·29).

INTERPRETATION

Oral switch antimicrobial therapy was non-inferior to intravenous standard therapy in participants with low-risk S aureus bloodstream infection. However, it is necessary to carefully assess patients for signs and symptoms of complicated S aureus bloodstream infection at the time of presentation and thereafter before considering early oral switch therapy.

FUNDING

Deutsche Forschungsgemeinschaft.

TRANSLATIONS

For the German, Spanish, French and Dutch translations of the abstract see Supplementary Materials section.

Oral Antibiotics for Bacteremia and Infective Endocarditis: Current Evidence and Future Perspectives

Bacteremia and endocarditis are two clinical syndromes that, for decades, were managed exclusively with parenteral antimicrobials, irrespective of a given patient's clinical condition, causative pathogen, or its antibiotic susceptibility profile. This clinical approach, however, was based on low-quality data and outdated expert opinions. When a patient's condition has improved, gastrointestinal absorption is not compromised, and an oral antibiotic regimen reaching adequate serum concentrations is available, a switch to oral antibacterials can be applied. Although available evidence has reduced the timing of the oral switch in bacteremia to three days/until clinical improvement, there are only scarce data regarding less than 10-day intravenous antibiotic therapy in endocarditis. Many standard or studied oral antimicrobial dosages are smaller than the approved doses for parenteral administration, which is a risk factor for treatment failure; in addition, the gastrointestinal barrier may affect drug bioavailability, especially when the causative pathogen has a minimum inhibitory concentration that is close to the susceptibility breakpoint. A considerable number of patients infected by such near-breakpoint strains may not be potential candidates for oral step-down therapy to non-highly bioavailable antibiotics like beta-lactams; different breakpoints should be determined for this setting. This review will focus on summarizing findings about pathogen-specific tailoring of oral step-down therapy for bacteremia and endocarditis, but will also present laboratory and clinical data about antibiotics such as beta-lactams, linezolid, and fosfomycin that should be studied more in order to elucidate their role and optimal dosage in this context.

Comparison of Oral and Intravenous Definitive Antibiotic Therapy for Beta-Hemolytic Streptococcus Species Bloodstream Infections from Soft Tissue Sources: a Propensity Score-Matched Analysis

Beta-hemolytic streptococci are common causes of bloodstream infection (BSI). There is emerging data regarding oral antibiotics for BSI but limited for beta-hemolytic streptococcal BSI. We conducted a retrospective study of adults with beta-hemolytic streptococcal BSI from a primary skin/soft tissue source from 2015 to 2020. Patients transitioned to oral antibiotics within 7 days of treatment initiation were compared to those who continued intravenous therapy, after propensity score matching. The primary outcome was 30-day treatment failure (composite of mortality, infection relapse, and hospital readmission). A prespecified 10% noninferiority margin was used for the primary outcome. We identified 66 matched pairs of patients treated with oral and intravenous antibiotics as definitive therapy. Based on an absolute difference in 30-day treatment failure of 13.6% (95% confidence interval 2.4 to 24.8%), the noninferiority of oral therapy was not confirmed (P = 0.741); on the contrary, the superiority of intravenous antibiotics is suggested by this difference. Acute kidney injury occurred in two patients who received intravenous treatment and zero who received oral therapy. No patients experienced deep vein thrombosis or other vascular complications related to treatment. In patients treated for beta-hemolytic streptococcal BSI, those who transitioned to oral antibiotics by day 7 showed higher rates of 30-day treatment failure than propensity-matched patients. This difference may have been driven by underdosing of oral therapy. Further investigation into optimal antibiotic choice, route, and dosing for definitive therapy of BSI is needed.

Oral stepdown in Gram-positive bloodstream infections: A step in the right direction

Bloodstream infections (BSIs) due to Gram-positive organisms have traditionally been treated with prolonged courses of intravenous antimicrobials. However, this dogma is associated with substantial burden to the patient and health care system. Consequently, there is growing interest in the utilization of oral stepdown therapy, defined as the transition of intravenous therapy to an active oral agent, for this indication. This review highlights available literature examining oral stepdown in adult patients with BSI due to commonly encountered Gram-positive pathogens, including Staphylococcus aureus, Streptococcus spp., and Enterococcus spp. Support for oral stepdown in this setting is primarily derived from observational studies subject to selection bias. Nevertheless, this treatment strategy exhibits promising potential in carefully selected patients as it is consistently associated with reductions in hospital length of stay without jeopardizing clinical cure or survivability. Prospective, randomized trials are needed for validation of oral stepdown in Gram-positive BSI and to identify the optimal patient population and regimen.

Uncomplicated Streptococcal Bacteremia: The Era of Oral Antibiotic Step-down Therapy?

BACKGROUND

The purpose of this study was to compare the clinical outcomes of adults with uncomplicated streptococcal bacteremia who received either oral (PO) step-down or continued intravenous (IV) therapy.

METHODS

This was a retrospective, single-center, cohort study, including adults admitted with Streptococcal bloodstream infection between January 1, 2013, and December 31, 2020. Only patients with uncomplicated Streptococcal bloodstream infections were included. Patients who transitioned to PO therapy within 5 days from bacteremia onset were compared to patients receiving continued IV therapy. The primary outcome was clinical failure, defined by either 90-day hospital readmission or mortality. Secondary outcomes included hospital length of stay (LOS) and antibiotic-related adverse events (AAEs).

RESULTS

Of the 264 patients included, 42% were transitioned to PO therapy. Group B Streptococcus (22.7%) was the most common isolate. The most common sources of infection were skin and soft tissue (35%) and pulmonary (25%). Intensive care unit (ICU) stay was more common in the continued IV therapy group (22.2%) than in the PO step-down group (5.4%). The frequency of clinical failure was similar in the IV and PO groups (24.2% vs. 18.0%, P=0.23). The IV group had longer hospital LOS (median, [interquartile range (IQR)]) compared with the PO group (7 [5-13.5] vs. 4 [3-5] days, P<0.001). The incidence of AAEs was similar in the IV and PO groups (1.3% vs. 1.8%, P=0.74).

CONCLUSION

Oral antibiotic step-down therapy may be appropriate for the treatment of uncomplicated Streptococcal bacteremia, with consideration of factors such as patient comorbidities, type of infection, source control and clinical progress.

Sequential oral antibiotic in uncomplicated Staphylococcus aureus bacteraemia: a propensity-matched cohort analysis

OBJECTIVES

We aimed to analyse the efficacy and safety of oral sequential therapy (OST) in uncomplicated Staphylococcus aureus bacteraemia (SAB).

METHODS

Single-centre observational cohort at a tertiary hospital in Spain, including all patients with the first SAB episode from January 2015 to December 2020. We excluded patients with complicated SAB and those who died during the first week. Patients were classified into the OST group (patients who received oral therapy after initial intravenous antibiotic therapy [IVT]), and IVT group (patients who received exclusively IVT). We performed a propensity-score matching to balance baseline differences. The primary composite endpoint was 90-day mortality or microbiological failure. Secondary endpoints included 90-day SAB relapse.

RESULTS

Out of 407 SAB first episodes, 230 (56.5%) were included. Of these, 112 (n = 48.7%) received OST and 118 (51.3%) IVT exclusively. Transition to oral therapy was performed after 7 days (interquartile range, 4-11). The primary endpoint occurred in 10.7% (11/112) in OST vs. 30.5% (36/118) in IVT (p < 0.001). SAB relapses occurred in 3.6% (4/112) vs. 1.7% (2/118) (p 0.436). None of the deaths in OST were related to SAB or its complications. After propensity-score matching, the primary endpoint was not more frequent in the OST group (relative risk, 0.42; 95% CI, 0.22-0.79). Ninety-day relapses occurred similarly in both groups (relative risk, 1.35; 95% CI, 0.75-2.39).

DISCUSSION

After an initial intravenous antibiotic, patients with uncomplicated SAB can safely be switched to oral antibiotics without apparent adverse outcomes. This strategy could save costs and complications of prolonged hospital stays. Prospective randomized studies are needed.

Impact of specialty on the self-reported practice of using oral antibiotic therapy for definitive treatment of bloodstream infections

Background:

No established guidelines exist regarding the role of oral antibiotic therapy (OAT) to treat bloodstream infections (BSIs), and practices may vary depending on clinician specialty and experience.

Objective:

To assess practice patterns regarding oral antibiotic use for treatment of bacteremia in infectious diseases clinicians (IDCs, including physicians and pharmacists and trainees in these groups) and non–infectious diseases clinicians (NIDCs).

Design:

Open-access survey.

Participants:

Clinicians caring for hospitalized patients receiving antibiotics.

Methods:

An open-access, web-based survey was distributed to clinicians at a Midwestern academic medical center using e-mail and to clinicians outside the medical center using social media. Respondents answered questions regarding confidence prescribing OAT for BSI in different scenarios. We used χ2 analysis for categorical data evaluated association between responses and demographic groups.

Results:

Of 282 survey responses, 82.6% of respondents were physicians, 17.4% pharmacists, and IDCs represented 69.2% of all respondents. IDCs were more likely to select routine use of OAT for BSI due to gram-negative anaerobes (84.6% vs 59.8%; P < .0001), Klebsiella spp (84.5% vs 69.0%; P < .009), Proteus spp (83.6% vs 71.3%; P < .027), and other Enterobacterales (79.5% vs 60.9%; P < .004). Our survey results revealed significant differences in selected treatment of Staphylococcus aureus syndromes. Fewer IDCs than NIDCs selected OAT to complete treatment for methicillin-resistant S. aureus (MRSA) BSI due to gluteal abscess (11.9% vs 25.6%; P = .012) and methicillin-susceptible S. aureus (MSSA) BSI due to septic arthritis (13.9% vs 20.9%; P = .219).

Conclusions:

Practice variation and discordance with evidence for the use of OAT for BSIs exists among IDCs versus NIDCs, highlighting opportunities for education in both clinician groups.

Early Transition to Oral Antimicrobial Therapy Among Children With Staphylococcus aureus Bacteremia and Acute Hematogenous Osteomyelitis

BACKGROUND

Staphylococcus aureus bacteremia (SAB) is a frequent complication of acute hematogenous osteomyelitis (AHO) in children, but data on the optimal duration of parenteral antibiotics prior to transition to oral antibiotics remains sparse. We examined clinical outcomes associated with early transition to oral antimicrobial therapy among children admitted to our institution with AHO and SAB, and evaluated the utility of a severity of illness score (SIS) to guide treatment decisions in this setting.

METHODS

Children with AHO and SAB admitted to our institution between January 1, 2009, and December 31, 2018, were retrospectively reviewed and stratified according to a previously validated SIS into mild (0-3), moderate (4-7) and severe (8-10) cohorts. Groups were assessed for differences in treatment (eg, parenteral and oral antibiotic durations, surgeries) and clinical response (eg, bacteremia duration, acute kidney injury, length of stay and treatment failure).

RESULTS

Among 246 children identified with AHO and SAB, median parenteral antibiotic duration differed significantly between mild (n = 80), moderate (n = 98) and severe (n = 68) cohorts (3.6 vs. 6.5 vs. 14.3 days; P ≤ 0.001). SIS cohorts also differed with regard to number of surgeries (0.4 vs. 1.0 vs. 2.1; P ≤ 0.001), duration of bacteremia (1.0 vs. 2.0 vs. 4.0 days; P ≤ 0.001), acute kidney injury (0.0% vs. 3.0% vs. 20.5%; P ≤ 0.001), hospital length of stay (4.8 vs. 7.4 vs. 16.4 days; P ≤ 0.001) and total duration of antibiotics (34.5 vs. 44.7 vs. 60.7 days; P ≤ 0.001). Early transition to oral antimicrobial therapy among mild or moderate SIS cohorts was not associated with treatment failure despite SAB.

CONCLUSIONS

SAB is associated with a wide range of illness among children with AHO, and classification of severity may be useful for guiding treatment decisions. Early transition to oral antimicrobial therapy appears safe in children with mild or moderate AHO despite the presence of SAB.

Comparison of Sequential Dalbavancin to Standard-of-Care Treatment for Staphylococcus aureus Bloodstream Infections

Background

Dalbavancin (DAL) is a long-acting lipoglycopeptide with activity against Staphylococcus aureus, including methicillin-resistant S. aureus (MRSA). This study investigates DAL as sequential therapy in S. aureus bloodstream infections (BSIs).

Methods

We conducted a retrospective cohort study from 2014 to 2021 comparing sequential DAL with standard-of-care therapy (SoC) for S. aureus BSI. The primary outcome was 90-day clinical failure (90-day all-cause mortality or 90-day recurrence). Secondary outcomes were incidence of acute kidney injury, creatinine phosphokinase elevations, catheter-related thrombosis, and hospital-acquired infections. Analyses were adjusted using inverse probability of treatment weighting (IPTW).

Results

Overall, 225 patients (45 DAL, 180 SoC) were included. DAL patients had a higher incidence of community-acquired infection and persons who use drugs; SoC patients had more comorbidities and a longer duration of bacteremia. MRSA incidence was similar between the DAL and SoC groups. The median length of stay was 16 days among DAL recipients compared with 24 days among SoC recipients. Central catheter placement was 17.8% compared with 57.2% in the SoC group. Ninety-day clinical failure occurred in 13.3% and 18.3% of participants in the DAL and SOC groups, respectively. In IPTW-adjusted analysis, sequential DAL was not associated with 90-day clinical failure (adjusted odds ratio, 0.94; 95% CI, 0.333–2.32).

Conclusions

This study provides preliminary evidence that select patients with S. aureus BSI treated with sequential DAL have similar clinical failure rates, with significant reductions in catheter placement and hospital length of stay compared with SoC. Further prospective evaluation is needed.

Oral step-down therapy in patients with uncomplicated Staphylococcus aureus primary bacteremia and catheter-related bloodstream infections

Patients with uncomplicated Staphylococcus aureus primary bacteremia and catheter-related bloodstream infection (CRBSI) should be treated for at least 14 days. However, evidence for oral step-down therapy is lacking in these patients. A retrospective cohort was identified from 2013 to 2018 in a 1,950-bed tertiary hospital. An oral antimicrobial therapy (OAT) group was defined as patients treated with oral antibiotics following less than 10 days of intravenous antimicrobial therapy (IAT). Treatment failure was defined as any case of recurrence or death within 90 days. A total of 103 patients were included in the analysis, including 32 patients treated with OAT. Rates of treatment failure were 3.2% and 12.7% in the OAT and IAT groups (P = 0.113). The length of hospital stay was shorter in the OAT group. OAT was not an independent risk factor for treatment failure. OAT may reduce the duration of hospitalization without adverse effects in these patients.

Intravenous versus Oral Step-Down for the Treatment of Staphylococcus aureus Bacteremia in a Pediatric Population

Limited data are available regarding optimal antimicrobial therapy for Staphylococcus aureus bacteremia (SAB) in pediatric patients. The purpose of this study was to assess clinical characteristics and outcomes associated with intravenous (IV) versus oral step-down treatment of pediatric SAB. This study evaluated patients aged 3 months to 18 years that received at least 72 h of inpatient treatment for SAB. The primary endpoint was 30-day readmission. Secondary endpoints included hospital length of stay and inpatient mortality. One hundred and one patients were included in this study. The median age was 7.9 years. Patients who underwent oral step-down were less likely to be immunocompromised and more likely to have community-acquired SAB from osteomyelitis or skin and soft tissue infection (SSTI). More patients in the IV therapy group had a 30-day readmission (10 (25.6%) vs. 3 (5.3%), p = 0.006). Mortality was low (5 (5%)) and not statistically different between groups. Length of stay was greater in patients receiving IV therapy only (11 vs. 7 days, p = 0.001). In this study, over half of the patients received oral step-down therapy and 30-day readmission was low for this group. Oral therapy appears to be safe and effective for patients with SAB from osteomyelitis or SSTIs.

How to investigate and manage a patient with a Staphylococcus aureus bacteraemia

Staphylococcus aureus bacteraemia is common, and associated with significant morbidity and mortality as a result of its high relapse rate and the risk of complicated infection. A positive blood culture for S. aureus should prompt a thorough patient assessment to identify a potential focus of infection, and the risk factors for the development or presence of complicated infection. Clinical management depends on the patient's characteristics and presenting features. This article gives a systematic approach to the patient with S. aureus bacteraemia, including points to look for on history and examination, the markers of complicated infection, and when to request transoesophageal echocardiography and further imaging. Treatment principles outlined include the rationale for choice of antibiotic treatment and need to involve infection specialists.

Population pharmacokinetics of free flucloxacillin in patients treated with oral flucloxacillin plus probenecid

Oral flucloxacillin may be coadministered with probenecid to reduce flucloxacillin clearance and increase attainment of pharmacokinetic-pharmacodynamic (PK/PD) targets. The aims of this study were to develop a population PK model of free flucloxacillin when administered orally with probenecid, and to identify optimal dosing regimens for this combination.

METHODS

We performed a prospective observational study of adults (45 participants) treated with oral flucloxacillin 1000 mg and probenecid 500 mg 8-hourly for proven or probable staphylococcal infections. Steady-state mid-dose-interval flucloxacillin measurements (45 concentrations) were combined with existing data from a crossover study of healthy participants receiving flucloxacillin with and without probenecid (11 participants, 363 concentrations). We developed a population pharmacokinetic model of free flucloxacillin concentrations within Monolix, and used Monte Carlo simulation to explore optimal dosing regimens to attain PK/PD targets proposed in the literature (free drug time above minimum inhibitory concentration).

RESULTS

Flucloxacillin disposition was best described by a 1-compartment model with a lag time and first-order absorption. Free flucloxacillin clearance depended on probenecid, allometrically-scaled fat free mass (FFM) and estimated glomerular filtration rate (eGFR). Predicted PK/PD target attainment was suboptimal with standard dosing regimens with flucloxacillin alone, but substantially improved in the presence of probenecid.

CONCLUSION

The simulation results reported can be used to identify dose regimens that optimise flucloxacillin exposure according to eGFR and FFM. Patients with higher FFM and eGFR may require the addition of probenecid and 6-hourly dosing to achieve PK/PD targets. The regimen was well-tolerated, suggesting a potential for further evaluation in controlled clinical trials to establish efficacy.

β-Lactams against the Fortress of the Gram-Positive Staphylococcus aureus Bacterium

The biological diversity of the unicellular bacteria-whether assessed by shape, food, metabolism, or ecological niche-surely rivals (if not exceeds) that of the multicellular eukaryotes. The relationship between bacteria whose ecological niche is the eukaryote, and the eukaryote, is often symbiosis or stasis. Some bacteria, however, seek advantage in this relationship. One of the most successful-to the disadvantage of the eukaryote-is the small (less than 1 μm diameter) and nearly spherical Staphylococcus aureus bacterium. For decades, successful clinical control of its infection has been accomplished using β-lactam antibiotics such as the penicillins and the cephalosporins. Over these same decades S. aureus has perfected resistance mechanisms against these antibiotics, which are then countered by new generations of β-lactam structure. This review addresses the current breadth of biochemical and microbiological efforts to preserve the future of the β-lactam antibiotics through a better understanding of how S. aureus protects the enzyme targets of the β-lactams, the penicillin-binding proteins. The penicillin-binding proteins are essential enzyme catalysts for the biosynthesis of the cell wall, and understanding how this cell wall is integrated into the protective cell envelope of the bacterium may identify new antibacterials and new adjuvants that preserve the efficacy of the β-lactams.

Early Oral Antibiotic Switch for Staphylococcus aureus Bacteremia: Many Are Called, but Few Are Chosen

Staphylococcus aureus bacteremia (SAB) is a complicated, high-risk disease. For selected low-risk SAB, the role of oral antibiotic stepdown therapy is unknown. Bupha-Intr et al. report a retrospective cohort of low-risk SAB patients who did well with a short duration of intravenous antibiotics, followed by an additional ∼10 days of oral antibiotics, primarily using beta-lactams. Prospective trials will help further define the efficacy of this approach.

A Narrative Review of Early Oral Stepdown Therapy for the Treatment of Uncomplicated Staphylococcus aureus Bacteremia: Yay or Nay?

Historically, intravenous (IV) antibiotics have been the cornerstone of treatment for uncomplicated Staphylococcus aureus bacteremia (SAB). However, IV antibiotics are expensive, increase the rates of hospital readmission, and can be associated with catheter-related complications. As a result, the potential role of oral antibiotics in the treatment of uncomplicated SAB has become a subject of interest. This narrative review article aims to summarize key arguments for and against the use of oral antibiotics to complete treatment of uncomplicated SAB and evaluates the available evidence for specific oral regimens. We conclude that evidence suggests that oral step-down therapy can be an alternative for select patients who meet the criteria for uncomplicated SAB and will comply with medical treatment and outpatient follow-up. Of the currently studied regimens discussed in this article, linezolid has the most support, followed by fluoroquinolone plus rifampin.