The BAF complex inhibitor pyrimethamine reverses HIV-1 latency in people with HIV-1 on antiretroviral therapy

Reactivation of the latent HIV-1 reservoir is a first step toward triggering reservoir decay. Here, we investigated the impact of the BAF complex inhibitor pyrimethamine on the reservoir of people living with HIV-1 (PLWH). Twenty-eight PLWH on suppressive antiretroviral therapy were randomized (1:1:1:1 ratio) to receive pyrimethamine, valproic acid, both, or no intervention for 14 days. The primary end point was change in cell-associated unspliced (CA US) HIV-1 RNA at days 0 and 14. We observed a rapid, modest, and significant increase in (CA US) HIV-1 RNA in response to pyrimethamine exposure, which persisted throughout treatment and follow-up. Valproic acid treatment alone did not increase (CA US) HIV-1 RNA or augment the effect of pyrimethamine. Pyrimethamine treatment did not result in a reduction in the size of the inducible reservoir. These data demonstrate that the licensed drug pyrimethamine can be repurposed as a BAF complex inhibitor to reverse HIV-1 latency in vivo in PLWH, substantiating its potential advancement in clinical studies.

HIV-1 resistance against dolutegravir fluctuates rapidly alongside erratic treatment adherence: a case report

OBJECTIVES

We report a case of incomplete HIV-1 suppression on a dolutegravir, lamivudine, and abacavir single-tablet regimen with the emergence of the H51Y and G118R integrase resistance mutations.

METHODS

Integrase sequencing was performed retrospectively by Sanger and next-generation sequencing. Rates of emergence and decline of resistance mutations were calculated using next-generation sequencing data. Dolutegravir plasma concentrations were measured by ultra-performance liquid chromatography-tandem mass spectrometry. The effects of H51Y and G118R on infectivity, fitness, and susceptibility to dolutegravir were quantified using cell-based assays.

RESULTS

During periods of non-adherence to treatment, mutations were retrospectively documented only by next-generation sequencing. Misdiagnosis by Sanger sequencing was caused by the rapid decline of mutant strains within the retroviral population. This observation was also true for a M184V lamivudine-resistant reverse transcriptase mutation found in association with integrase mutations on single HIV genomes. Resistance rebound upon treatment re-initiation was swift (>8000 copies per day). Next-generation sequencing indicated cumulative adherence to treatment. Compared to WT HIV-1, relative infectivity was 73%, 38%, and 43%; relative fitness was 100%, 35%, and 10% for H51Y, G118R, and H51Y+G118R viruses, respectively. H51Y did not change the susceptibility to dolutegravir, but G188R and H51Y+G118R conferred 7- and 28-fold resistance, respectively.

CONCLUSION

This case illustrates how poorly-fit drug-resistant viruses wax and wane alongside erratic treatment adherence and are easily misdiagnosed by Sanger sequencing. We recommend next-generation sequencing to improve the clinical management of incomplete virological suppression with dolutegravir.

A highly virulent variant of HIV-1 circulating in the Netherlands

We discovered a highly virulent variant of subtype-B HIV-1 in the Netherlands. One hundred nine individuals with this variant had a 0.54 to 0.74 log₁₀ increase (i.e., a ~3.5-fold to 5.5-fold increase) in viral load compared with, and exhibited CD4 cell decline twice as fast as, 6604 individuals with other subtype-B strains. Without treatment, advanced HIV-CD4 cell counts below 350 cells per cubic millimeter, with long-term clinical consequences-is expected to be reached, on average, 9 months after diagnosis for individuals in their thirties with this variant. Age, sex, suspected mode of transmission, and place of birth for the aforementioned 109 individuals were typical for HIV-positive people in the Netherlands, which suggests that the increased virulence is attributable to the viral strain. Genetic sequence analysis suggests that this variant arose in the 1990s from de novo mutation, not recombination, with increased transmissibility and an unfamiliar molecular mechanism of virulence.

Added value of 18F-FDG-PET/CT and cardiac CTA in suspected transcatheter aortic valve endocarditis

BACKGROUNDS

Transcatheter-implanted aortic valve infective endocarditis (TAVI-IE) is difficult to diagnose when relying on the Duke Criteria. Our aim was to assess the additional diagnostic value of 18F-fluorodeoxyglucose (18F-FDG) positron emission/computed tomography (PET/CT) and cardiac computed tomography angiography (CTA) in suspected TAVI-IE.

METHODS

A multicenter retrospective analysis was performed in all patients who underwent 18F-FDG-PET/CT and/or CTA with suspected TAVI-IE. Patients were first classified with Duke Criteria and after adding 18F-FDG-PET/CT and CTA, they were classified with European Society of Cardiology (ESC) criteria. The final diagnosis was determined by our Endocarditis Team based on ESC guideline recommendations.

RESULTS

Thirty patients with suspected TAVI-IE were included. 18F-FDG-PET/CT was performed in all patients and Cardiac CTA in 14/30. Using the Modified Duke Criteria, patients were classified as 3% rejected (1/30), 73% possible (22/30), and 23% definite (7/30) TAVI-IE. Adding 18F-FDG-PET/CT and CTA supported the reclassification of 10 of the 22 possible cases as "definite TAVI-IE" (5/22) or "rejected TAVI-IE" (5/22). This changed the final diagnosis to 20% rejected (6/30), 40% possible (12/30), and 40% definite (12/30) TAVI-IE.

CONCLUSIONS

Addition of 18F-FDG-PET/CT and/or CTA changed the final diagnosis in 33% of patients and proved to be a valuable diagnostic tool in patients with suspected TAVI-IE.

High Treatment Uptake in Human Immunodeficiency Virus/Hepatitis C Virus-Coinfected Patients After Unrestricted Access to Direct-Acting Antivirals in the Netherlands

Background

The Netherlands has provided unrestricted access to direct-acting antivirals (DAAs) since November 2015. We analyzed the nationwide hepatitis C virus (HCV) treatment uptake among patients coinfected with human immunodeficiency virus (HIV) and HCV.

Methods

Data were obtained from the ATHENA HIV observational cohort in which >98% of HIV-infected patients ever registered since 1998 are included. Patients were included if they ever had 1 positive HCV RNA result, did not have spontaneous clearance, and were known to still be in care. Treatment uptake and outcome were assessed. When patients were treated more than once, data were included from only the most recent treatment episode. Data were updated until February 2017. In addition, each treatment center was queried in April 2017 for a data update on DAA treatment and achieved sustained virological response.

Results

Of 23574 HIV-infected patients ever linked to care, 1471 HCV-coinfected patients (69% men who have sex with men, 15% persons who [formerly] injected drugs, and 15% with another HIV transmission route) fulfilled the inclusion criteria. Of these, 87% (1284 of 1471) had ever initiated HCV treatment between 2000 and 2017, 76% (1124 of 1471) had their HCV infection cured; DAA treatment results were pending in 6% (92 of 1471). Among men who have sex with men, 83% (844 of 1022) had their HCV infection cured, and DAA treatment results were pending in 6% (66 of 1022). Overall, 187 patients had never initiated treatment, DAAs had failed in 14, and a pegylated interferon-alfa-based regimen had failed in 54.

Conclusions

Fifteen months after unrestricted DAA availability the majority of HIV/HCV-coinfected patients in the Netherlands have their HCV infection cured (76%) or are awaiting DAA treatment results (6%). This rapid treatment scale-up may contribute to future HCV elimination among these patients.

[Infections during glucocorticoid use]

Glucocorticoid treatment increases the risk of opportunistic infection. Infections that can arise during glucocorticoid use, and for which preventative measures can be taken, include reactivation of latent tuberculosis and hepatitis B, pneumococcal and Pneumocystis jiroveci pneumonia, influenza, herpes zoster and Strongyloides stercoralis hyperinfection syndrome. The risk of such infections depends upon the duration of glucocorticoid use and dosage, as well as comorbidity and comedication. It is important to enquire about vaccinations, travel, exposure and previous infections when taking a case history. Possible infectious complications should be considered in patients who are receiving high-dose glucocorticoids treatment amounting to more than 420 mg PED per 4 weeks. Preventative measures are not usually required in patients who receive a short high-dosed treatment (30 mg PED in 7 days) or prednisolone at a dosage of < 15 mg/day.

The impact of infections on delisting patients from the liver transplantation waiting list

Approximately 20% of the patients listed for liver transplantation die before transplantation can be accomplished. Understanding risk factors for waiting list mortality may help to improve survival and organ allocation. Infections are very common in patients with cirrhosis and are associated with significant morbidity and mortality. This study analysed the frequency and characteristics of infections in patients awaiting liver transplantation, identified risk factors for withdrawal from the waiting list and evaluated the impact of infections on the clinical outcome. A retrospective analysis of consecutive patients listed for liver transplantation in Rotterdam, the Netherlands from 2007 to 2014 was conducted. Infections occurred in 144 of 327 studied patients (44%). In this cohort, 23.4% of the patients on the liver transplantation waiting list were delisted or died before transplantation. Patients with an infection were 5.2 times more likely to become delisted than noninfected patients. In the 30 days after the first infection, patients were 33.8 times more likely to become delisted compared to noninfected patients. High age, high MELD score, refractory ascites and inappropriate antibiotic therapy were independent predictors for delisting due to infection. Infections occur frequently in patients on the liver transplantation waiting list. Emphasis on appropriate and timely antimicrobial therapy is required.

Dolutegravir as maintenance monotherapy: first experiences in HIV-1 patients

BACKGROUND

Dolutegravir is recommended as part of combination ART (cART) for HIV-1-infected patients. Toxicities, drug interactions and costs related to cART still warrant the search for improved treatment options. Dolutegravir's high resistance barrier might make it suitable as antiretroviral maintenance monotherapy. The feasibility of this strategy is currently unknown.

METHODS

This is a prospective case series on five consecutive HIV-1-infected patients on cART without previous virological failure who switched to dolutegravir monotherapy. All were HIV-RNA suppressed <50 copies/mL and had contraindications to current and alternative combinations of antiretroviral drugs. HIV-RNA was measured at baseline, week 4, week 8, week 12 and every 6 weeks thereafter. Patients would be switched back to their original cART upon confirmed HIV-RNA >50 copies/mL.

RESULTS

The five patients had been HIV-RNA suppressed <50 copies/mL for ≥1.5 years prior to the initiation of dolutegravir monotherapy. All were on NNRTI-containing regimens at the switch. HIV-RNA remained <50 copies/mL at all timepoints in four patients. One patient, with end-stage renal disease and on calcium supplements, had a pre-cART HIV-RNA of 625 000 copies/mL with a CD4 nadir of 120 cells/mm(3) and had HIV-RNA of 8150 copies/mL at week 30. The dolutegravir Ctrough was 0.18 mg/L. This patient did not have acquired resistance or evidence of adherence problems and HIV-RNA was resuppressed after switching to his former cART.

CONCLUSIONS

This case series indicates that dolutegravir monotherapy might be a valuable maintenance option in selected HIV-infected patients who are well suppressed on cART, if confirmed by future randomized clinical trials.

Point prevalence of appropriate antimicrobial therapy in a Dutch university hospital

Antimicrobial stewardship teams have been shown to increase appropriate empirical antibiotic therapy and reduce medical errors and costs in targeted populations, but the effect in non-targeted populations is still unclear. The aim of this study was to determine the prevalence of inappropriate antibiotic use in a large university hospital and identify areas in which antimicrobial stewardship will be the most effective. In a point prevalence survey we assessed the appropriateness of antibiotic therapy using an electronic surveillance system in combination with a standardized method for duration of therapy, dosage, dosage interval, route of administration, and choice of antibiotic drug. Patients using at least one antibiotic drug were included. Among 996 patients admitted in the surveyed wards, 337 patients (33.8 %) used one or more antibiotic drugs. Two hundred and twenty-one patients (22.2 %) used antibiotic medication therapeutically, with a total of 307 antibiotic prescriptions. Antibiotic therapy was deemed inappropriate in 90 (29.3 %) of these prescribed antibiotics, with an unjustified prescription as the most common reason for an inappropriate prescription. Use of fluoroquinolones and amoxicillin/clavulanic acid and a presumed diagnosis of fever of unknown origin, urinary tract infection, and respiratory tract infection were associated with inappropriate antibiotic therapy. Our study provides insight into the (in)appropriateness of antibiotic prescriptions in a tertiary care center in the Netherlands and identifies areas for improvement. The use of an electronic surveillance system for this point prevalence study is easy and may serve as a baseline measurement for the future effect of antibiotic stewardship.

Modelling treatment effects in a clinical Bayesian network using Boolean threshold functions

OBJECTIVE

Appropriate antimicrobial treatment of infections in critically ill patients should be started as soon as possible, as delay in treatment may reduce a patient's prognostic outlook considerably. Ventilator-associated pneumonia (VAP) occurs in patients in intensive care units who are mechanically ventilated and is almost always preceded by colonisation of the respiratory tract by the causative microorganisms. It is very difficult to clinically diagnose VAP and, therefore, some form of computer-based decision support might be helpful for the clinician.

MATERIALS AND METHODS

As diagnosing and treating VAP involves reasoning with uncertainty, we have used a Bayesian network as the primary tool for building a decision-support system. The effects of usage of antibiotics on the colonisation of the respiratory tract by various pathogens and the subsequent antibiotic choices in case of VAP were modelled using the notion of causal independence. In particular, the conditional probability distribution of the random variable that represents the overall coverage of pathogens by antibiotics was modelled in terms of the conjunctive effect of the seven different pathogens, usually referred to as the noisy-AND model. In this paper, we investigate different coverage models, as well as generalisations of the noisy-AND, called noisy-threshold models, and test them on clinical data of intensive care unit (ICU) patients who are mechanically ventilated.

RESULTS

Some of the constructed noisy-threshold models offered further improvement of the performance of the Bayesian network in covering present causative pathogens by advising appropriate antimicrobial treatment.

CONCLUSIONS

By reconsidering the modelling of interactions between the random variables in a Bayesian network using the theory of causal independence, it is possible to refine its performance. This was clearly shown for our Bayesian network concerning VAP, indicating that only specific noisy-threshold models might be appropriate for the modelling of the interaction between pathogens and antimicrobial treatment with respect to susceptibility. The results obtained also provide evidence that the noisy-OR and noisy-AND might not always be the best functions to model interactions among random variables.

Predicting pathogens causing ventilator-associated pneumonia using a Bayesian network model

BACKGROUND

We previously validated a Bayesian network (BN) model for diagnosing ventilator-associated pneumonia (VAP). Here, we report on the performance of the model to predict microbial causes of VAP and to select antibiotics.

METHODS

Pathogens were grouped into seven categories based upon the antibiotic susceptibility and epidemiological characteristics. Colonization of the upper respiratory tract was modelled in the BN and depended--in additional steps--on (i) duration of admission and ventilation, (ii) previous culture results and (iii) previous antibiotic use. A database with 153 VAP episodes and their microbial causes was used as reference standard. Appropriateness of antibiotic prescription, with fixed choices for pathogens predicted, was determined.

RESULTS

One hundred and seven VAP episodes were monobacterial and 46 were caused by two pathogens. Using duration of admission and ventilation only, areas under the receiver operating curve (AUC) ranged from 0.511 to 0.772 for different pathogen groups, and model predictions significantly improved when adding information on culture results, but not when adding information on antibiotic use. The best performing model (with all information) had AUC values ranging from 0.859 for Acinetobacter spp. to 0.929 for Streptococcus pneumoniae. With this model, 91 (85%) and 29 (63%) of all pathogen groups were correctly predicted for monobacterial and polymicrobial VAP, respectively. With fixed antibiotic choices linked to pathogen groups, 92% of all episodes would have been treated appropriately.

CONCLUSIONS

The BN models' performance to predict pathogens causing VAP improved markedly with information on colonization, resulting in excellent pathogen prediction and antibiotic selection. Prospective external validation is needed.

A Bayesian decision-support system for diagnosing ventilator-associated pneumonia

OBJECTIVE

To determine the diagnostic performance of a Bayesian Decision-Support System (BDSS) for ventilator-associated pneumonia (VAP).

DESIGN

A previously developed BDSS, automatically obtaining patient data from patient information systems, provides likelihood predictions of VAP. In a prospectively studied cohort of 872 ICU patients, VAP was diagnosed by two infectious-disease specialists using a decision tree (reference diagnosis). After internal validation daily BDSS predictions were compared with the reference diagnosis. For data analysis two approaches were pursued: using BDSS predictions (a) for all 9422 patient days, and (b) only for the 238 days with presumed respiratory tract infections (RTI) according to the responsible physicians.

MEASUREMENTS AND RESULTS

157 (66%) of 238 days with presumed RTI fulfilled criteria for VAP. In approach (a), median daily BDSS likelihood predictions for days with and without VAP were 77% [Interquartile range (IQR) = 56-91%] and 14% [IQR 5-42%, p < 0.001, Mann-Whitney U-test (MWU)], respectively. In receiver operating characteristics (ROC) analysis, optimal BDSS cut-off point for VAP was 46%, and with this cut-off point positive predictive value (PPV) and negative predictive value (NPV) were 6.1 and 99.6%, respectively [AUC = 0.857 (95% CI 0.827-0.888)]. In approach (b), optimal cut-off for VAP was 78%, and with this cut-off point PPV and NPV were 86 and 66%, respectively [AUC = 0.846 (95% CI 0.794-0.899)].

CONCLUSIONS

As compared with the reference diagnosis, the BDSS had good test characteristics for diagnosing VAP, and might become a useful tool for assisting ICU physicians, both for routinely daily assessment and in patients clinically suspected of having VAP. Empirical validation of its performance is now warranted.

[Post-exposure prophylaxis following exposure to HIV: adaptation to the situation may be indicated]

A woman aged 36 injured herself on a needle that had been used to take an iliac-crest biopsy from an HIV-positive patient and a man aged 34 and a woman aged 35 had sexual contact with their HIV-positive partners during which the condom tore. They were given post-exposure prophylaxis (PEP) which was formulated using medication and virus resistance data from the HIV-positive individual. At 3 and 6 months the patients were all still HIV-negative. After occupational or non-occupational exposure to HIV, PEP is initiated if there is a reasonable risk of transmission of HIV. In The Netherlands a combination of 3 antiretroviral drugs is advised based on demonstrated antiviral effectiveness in the regular treatment of HIV-infections. Frequently a standard PEP-regimen is prescribed. If the source patient has a history of antiretroviral therapy, the virus might be resistant to standard PEP-regimens. In these cases the choice of drugs in the PEP-regimen can be individualised based on the antiretroviral medication history of the source patient and known resistance patterns of the source virus.

Computer-assisted decision support for the diagnosis and treatment of infectious diseases in intensive care units

Diagnosing nosocomial infections in critically ill patients admitted to intensive care units (ICUs) is a challenge because signs and symptoms are usually non-specific for a particular infection. In addition, the choice of treatment, or the decision not to treat, can be difficult. Models and computer-based decision-support systems have been developed to assist ICU physicians in the management of infectious diseases. We discuss the historical development, possibilities, and limitations of various computer-based decision-support models for infectious diseases, with special emphasis on Bayesian approaches. Although Bayesian decision-support systems are potentially useful for medical decision making in infectious disease management, clinical experience with them is limited and prospective evaluation is needed to determine whether their use can improve the quality of patient care.

Do cultures contribute to optimisation of antibiotic therapy in the intensive care unit?

Obtaining diagnostic microbiological cultures before initiating empirical antimicrobial therapy is part of the diagnostic work-up of intensive care patients with a clinical suspicion of infection. However, it is unknown to what extent these cultures provide a microbiological cause of infection and to what extent antimicrobial therapy is influenced. During a 6-month period, all episodes of suspected clinical infection were analysed and categorised as non-microbiologically proven infection (non-MPI) or MPI. Effects of culture results on antibiotic therapy were analysed for episodes of respiratory tract infection. Invasive diagnostic techniques were not routinely used for diagnosis of respiratory tract infections. Among 212 patients admitted, 147 episodes of clinical suspicion of infection were recorded (104 for respiratory tract infection) and 1147 microbiological cultures were obtained (0.64 culture per patient day). Antibiotics were administered on 1111 (62%) of 1803 patients days. Of the respiratory tract infections, 571 cultures resulted in 49 (47%) MPI. Cover with empirical antibiotics was inappropriate in 7 of 104 cases (8%) of respiratory infections. In 12 cases (11.5%) empirical therapy could have been changed based on culture results. Negative cultures were never followed by cessation of therapy, but the duration of treatment was significantly shorter for non-MPI. Forty-seven percent of respiratory tract infections were microbiologically confirmed and, based on culture results, empirical antimicrobial therapy could have been influenced in 11.5% of cases of respiratory tract infections. These findings provide aspects to evaluate and improve the diagnostic work-up of infections in the ICU.

Resistance of uropathogens in symptomatic urinary tract infections in León, Nicaragua

Management of urinary tract infections (UTI) in Central America and especially Nicaragua, is complicated by the lack of knowledge about the antibiotic resistance of uropathogens. We conducted a prevalence study to gain more insight into the aetiology, bacterial resistance and risk factors for symptomatic UTI in the region of León, Nicaragua. In 2002, all consecutive patients with UTI symptoms and pyuria >/=10 WBC/hpf were admitted to the study. Positive cultures from midstream urine specimens were defined as >/=10(5) cfu/ml of a single uropathogen. Susceptibility tests were performed with disc diffusion tests using the Kirby-Bauer method and broth microdilution using National Committee for Clinical Laboratory Standards criteria both in León and a reference laboratory in Utrecht. A positive culture was present in 62 of 208 study subjects (30%). Escherichia coli (56%), Klebsiella spp. (18%) and Enterobacter spp. (11%) were the most frequent pathogens isolated. Presence of cystocele, incontinence and increasing age were risk factors for bacterial UTI. E. coli was least resistant to ceftriaxone, amikacin and nitrofurantoin (>90% susceptible). We observed high resistance rates in E. coli to amoxicillin (82%, MIC(90) 128 mg/l), trimethoprim-sulphamethoxazole (TMP-SMX) (64%, MIC(90) 32 mg/l), cephalothin (58%, MIC(90), 32 mg/l), ciprofloxacin (30%; MIC(90), 32 mg/l), amoxicillin/clavulanate (21%, MIC(90) 8 mg/l) and gentamicin (12%, MIC(90) 2 mg/l). Our results suggests that community acquired uropathogens in Nicaragua are highly resistant to many antimicrobial agents. The use of amoxicillin, trimethoprim-sulphamethoxazole and cephalothin against uropathogens needs to be reconsidered. High quinolone resistance rates among E. coli in Nicaragua gives cause for great concern.

Clinical pulmonary infection score for ventilator-associated pneumonia: accuracy and inter-observer variability

OBJECTIVE

Although quantitative microbiological cultures of samples obtained by bronchoscopy are considered the most specific tool for diagnosing ventilator-associated pneumonia, this labor-intensive invasive technique is not widely used. The Clinical Pulmonary Infection Score (CPIS), a diagnostic algorithm that relies on easily available clinical, radiographic, and microbiological criteria, could be an attractive alternative for diagnosing ventilator-associated pneumonia. Initially, the CPIS scoring system was validated upon 40 quantitative cultures of bronchoalveolar lavage fluid from 28 patients, and only few other studies have evaluated this scoring system since then. Therefore, little is known about the accuracy of this score.

DESIGN

We compared the scores of a slightly adjusted CPIS with results from quantitative cultures of bronchoalveolar lavage fluid in 99 consecutive patients with suspicion of ventilator-associated pneumonia, using growth of > or =10(4) cfu/ml in bronchoalveolar lavage fluid as a cut-off for diagnosing ventilator-associated pneumonia. In addition, the CPIS were calculated for 52 patients by two different intensivists to determine the inter-observer variability.

RESULTS

Ventilator-associated pneumonia was diagnosed in 69 (69.6%) patients. When using a CPIS >5 as diagnostic cutoff, the sensitivity of the score was 83% and its specificity was 17%. The area under the Receiver Operating Characteristic curve was 0.55. The level of agreement for prospectively measured Clinical Pulmonary Infection Score (< or =6 and >6) was poor (kappa =0.16).

CONCLUSIONS

When compared to quantitative cultures of bronchoalveolar lavage fluid, the CPIS has a low sensitivity and specificity for diagnosing ventilator-associated pneumonia with considerable inter-observer variability.

Double-blind, placebo-controlled study comparing the effect of azithromycin with clarithromycin on oropharyngeal and bowel microflora in volunteers

The purpose of this double-blind study was to assess the effect of azithromycin and clarithromycin on oral and fecal microflora. Bacterial species from fecal samples and throat washes from healthy volunteers were identified and quantified before, during and after receipt of either placebo ( n=6), azithromycin (500 mg once daily for 3 days; n=6) or clarithromycin (500 mg twice daily for 7 days; n=6). In both antibiotic groups, the changes in oropharyngeal aerobic microflora following antibiotic administration were minor. Antibiotics neither changed the bacterial load of Streptococcus spp. compared with placebo, nor did macrolide-resistant streptococci emerge. In the fecal aerobic microflora, the number of organisms of the family Enterobacteriaceae decreased slightly after antibiotic administration in both the clarithromycin and the azithromycin groups, but levels normalized by day 21 after therapy. No colonization with nonfermenters or Clostridium difficile was seen, and the total number of anaerobic bacteria was not affected in any study group. In conclusion, there were no significant differences between azithromycin and clarithromycin in their effect on human oropharyngeal and intestinal microflora, nor was the use of these antibiotics associated with colonization by resistant, gram-positive organisms or overgrowth of opportunistic microorganisms.