Fifteen-year experience with bloodstream isolates of coagulase-negative staphylococci in neonatal intensive care

Understanding Bacterial Isolates in Blood Culture and Approaches Used to Define Bacteria as Contaminants: A Literature Review

BACKGROUND

Interpretation of blood culture isolates is challenging due to a lack of standard methodologies for identifying contaminants. This problem becomes more complex when the specimens are from sick young infants, as a wide range of bacteria can cause illness among this group.

METHODS

We used 43 key words to find articles published between 1970 and 2011 on blood culture isolates and possible contaminants in the PubMed database. Experts were also consulted to obtain other relevant articles. Selection of articles followed systematic methods considering opinions from more than 1 reviewer.

RESULTS

After reviewing the titles of 3869 articles extracted from the database, we found 307 relevant to our objective. Based on the abstracts, 42 articles were selected for the literature review. In addition, we included 7 more articles based on cross-references and expert advice. The most common methods for differentiating blood culture isolates were multiple blood cultures from the same subject, antibiograms and molecular testing. Streptococcus pneumoniae, Hemophilus influenzae, Neisseria meningitidis and group A and B streptococcus were always considered as pathogens, whereas Bacillus sp., Diphtheroids, Propionibacterium and Micrococcus were commonly regarded as contaminants. Coagulase-negative staphylococci were the most frequent isolates and usually reported as contaminants unless the patient had a specific condition, such as long-term hospitalization or use of invasive devices (catheters).

CONCLUSIONS

Inaccurate interpretation of blood culture may falsely guide treatment and also has long-term policy implications. The combination of clinical and microbiological knowledge, patient's clinical history and laboratory findings are essential for appropriate interpretation of blood culture.

Routine skin cultures in predicting sepsis pathogens among hospitalized preterm neonates in Bangladesh

BACKGROUND

Few studies from developing countries have examined sensitivity, specificity, positive and negative predictive values of routine surface cultures.

OBJECTIVES

The purpose of the study was to determine sensitivity, specificity, and positive predictive value (PPV) of skin cultures among preterm neonates admitted to Dhaka Shishu Hospital, Bangladesh.

METHODS

The study was nested within a prospective, randomized, controlled trial of emollient treatment in Dhaka Shishu Hospital, Bangladesh. A total of 497 preterm infants <33 weeks gestational age and <72 h of chronological age were enrolled, and the sensitivity, specificity, and PPV of skin cultures were analyzed among 3,765 blood-skin culture pairs, wherein the skin culture was obtained within 13 days before the blood culture.

RESULTS

Overall sensitivity, specificity, and PPV were 16, 38, and 5%, respectively. PPV during Klebsiella pneumoniae outbreaks was about 9%, and the inguinal site had the highest PPV (6%) among the three skin sites. Acinetobacter spp.- and K. pneumoniae-specific PPVs were 28 and 23%, respectively. PPV was <2% for Candida spp., Enterobacter spp., and Salmonella spp.

CONCLUSION

Routine skin culture is inefficient in predicting the pathogen responsible for sepsis among premature neonates, even in a developing country setting, where the burden of bacterial infection is relatively high. Skin cultures are also of limited utility during K. pneumoniae outbreaks, and are not recommended.

Retained central venous lines in the newborn: report of one case and systematic review of the literature

The use of percutaneously inserted central catheters (PICCs) is an established practice in most NICUs. With the widespread use of these catheters, an increasing number of PICC complications has been reported in neonates. We present one case of a PICC retained and tethered in the vein in a very low birth weight infant, as well as a systematic review of PICC retention cases. Ten previous cases of PICC retention in neonates were found. Among those cases, the most common associated factors were coagulase-negative staphylococcus catheter colonization/bactcremia and long duration of catheterization. Occlusion was not a usefiul sign for predicting catheter retention. Once retention was established, heparin or urokinase instillations were ineffective. Although surgical exploration was sometimes required, firm, continuous traction applied to the catheter over several hours or intermittent, moderately strong pulling maneuvers were successful in 44.4 percent of the cases in which they were performed. Traction did not show major side effects. Our case provides additional support for use of traction as the initial approach in the management of this rare complication.

A study of the role of multiple site blood cultures in the evaluation of neonatal sepsis

BACKGROUND

The optimal number of blood cultures needed to document sepsis in an ill neonate has undergone little critical evaluation. Multiple site cultures may improve pathogen detection if intermittent bacteremia occurs, or if a low density of bacteria is present in the blood. We hypothesized, however, that bacterial clearance is slower and bacteremia more continuous in septic neonates, so that a single site blood culture should be sufficient to accurately document true septicemia.

OBJECTIVE

To determine the need for multiple site blood cultures in the evaluation of neonates for sepsis.

DESIGN/METHODS

Clinical data were prospectively collected for 216 neonates who had 269 pairs of blood cultures taken from two different peripheral sites for the evaluation of possible sepsis. A minimum of 1 ml of blood was obtained from the two peripheral sites within 15-30 min of each other. Based on prior retrospective data, we determined that 203 infants would need to have two site blood cultures to demonstrate a significant improvement in pathogen detection at an alpha of 0.05 and a beta of 0.20 (80%) power.

RESULTS

A total of 186 culture pairs were taken for evaluation of early-onset sepsis in 186 neonates, while 83 pairs were drawn for evaluation of late-onset sepsis in 43 neonates. In all, 21 neonates from the late-onset group were evaluated more than once, and 12 neonates were evaluated for both early- and late-onset sepsis. In all, 20 (9.2%) of 216 neonates had 22 episodes of culture-proven sepsis at a median age of 18 days. All neonates with positive cultures had the same organism with a similar sensitivity pattern obtained from the two different peripheral sites. The other 196 study neonates had negative blood cultures from both sites. The single episode of early-onset sepsis was caused by Listeria monocytogenes, while all remaining episodes were late-onset with the following organisms: Staphylococcus epidermidis (7), methicillin-resistant Staphylococcus aureus (MRSA) (3), combined MRSA and Candida albicans (2), Candida albicans alone (2), late-onset Group B beta-hemolytic Streptococcus (GBS) (2), Klebsiella pneumoniae (2), Enterococcus fecalis (1), Escherichia coli (1), and Serratia marcescens (1). Since no infant grew organisms from only one of the two sites, the data indicate that the diagnosis of sepsis would have been made correctly in all infants with a single site culture.

CONCLUSIONS

Two site blood cultures for the initial evaluation of neonatal sepsis do not have a better yield in pathogen detection. Sepsis in neonates can be detected with no loss of accuracy with a single site blood culture with blood volume of>or=1 ml.

Late-onset septicemia in a Norwegian national cohort of extremely premature infants receiving very early full human milk feeding

OBJECTIVES

To investigate the occurrence of and risk factors for late-onset septicemia (LOS) in a national cohort of extremely premature infants who received very early full human milk feeding.

METHODS

A prospective study of all infants born in Norway in 1999 and 2000 with gestational age of <28 weeks or birth weight of <1000 g was performed. Extensive clinical information, including data on feeding practices and episodes of septicemia, was collected on predefined forms. LOS was defined as growth of bacteria or fungi in blood cultures in conjunction with clinical symptoms consistent with systemic infection occurring after day 6 of life. Cox regression models, including models allowing for time-dependent covariates, were applied in the analysis of LOS.

RESULTS

Of 464 eligible infants, 462 (99.6%) were enrolled and 405 (87.7%) survived until day 7. LOS was diagnosed for 80 (19.7%). The predominant pathogens were coagulase-negative staphylococci, followed by Candida spp. Case fatality rates associated with septicemia were 10% in general and 43% for Candida spp septicemia. Necrotizing enterocolitis or bowel perforation was diagnosed for 19 infants (4%). Enteral feeding with human milk was initiated within the third day for 98% of patients, and 92% were receiving full enteral feeding (FEF) with human milk within the third week. Both high Clinical Risk Index for Babies scores and an umbilical venous catheter in situ at 7 days of age significantly predicted LOS. However, the overall most influential risk factor for LOS was the number of days without establishment of FEF with human milk, with an adjusted relative risk of 3.7 (2.0-6.9) for LOS if FEF was not established within the second week of life.

CONCLUSIONS

The incidence and case fatality rate of septicemia for this cohort of extremely preterm infants were lower than values in comparable studies. The main difference, compared with other studies, was the feeding practice, and the data suggest that very early FEF with human milk significantly reduces the risk of LOS among extremely premature infants.

Bacteriology in Patients with Chronic Sinusitis who have been Medically and Surgically Treated

Chronic sinusitis is a disease that afflicts a significant percentage of the population and causes considerable long-term morbidity. The common use of multiple broad-spectrum oral antibiotics and endoscopic sinus surgery to treat this condition may alter the pathogenes that promote persistence of chronic sinusitis. Forty-eight culture-positive patients with chronic sinusitis who had been medically treated for at least 3 months and had undergone sinus surgery were bacteriologically evaluated. Swab specimens of the middle meatus and sphenoethmoid recess were aseptically obtained endoscopically and cultured for aerobes. Coagulase-negative staphylococci were the most common isolates (45.8%), followed by Streptococcus pneumoniae (16.7%), Enterobacteriaceae (16.7%), Staphylococcus aureus (10.4%), and Pseudomonas aeruginosa (10.4%). Coagulase-negative staphylococci were the most frequently isolated organisms in our study, as in many other studies. Despite the significant predominance of these organisms, they have always been assumed to be contaminants, and their presence in culture has been discounted. Coagulase-negative S aureus may be a pathogen in the chronic sinusitis process, and sensitivities of this isolate should be obtained for evaluation and possible treatment of the disease.

Survey of methicillin-resistant coagulase-negative staphylococci isolated from the fingers of nursing students

To clarify the state of methicillin-resistant coagulase-negative staphylococci (MRCNS) contamination in the hospital environment, we compared MRCNS isolated from the fingers of 40 nursing students who had not yet experienced clinical practice and 40 who had just completed clinical practice in the hospital. Fourteen MRCNS strains were detected in 13 students (32.5%) after clinical practice; Staphylococcus epidermidis in 9 students, Staphylococcus haemolyticus in 3, and Staphylococcus saprophyticus in 2. Drug sensitivity tests were performed, and the minimum inhibitory concentration (MIC) of penicillin-G (PCG) was more than 2 microg/ml in all strains, and that of ampicillin (ABPC) was more than 16 microg/ml in many strains. Only a few strains showed high MIC values for the other drugs tested. However, some Staphylococcus haemolyticus strains showed high MIC values for cefazolin (CEZ), arbekacin (ABK), gentamicin (GM), ofloxacin (OFLX), or imipenem (IPM). In all strains, the mecA gene was detected by polymerase chain reaction (PCR), and penicillin binding protein 2' (PBP2') was detected by the latex agglutination method. Methicillin-resistant Staphylococcus epidermidis (MRSE) isolated from the fingers of nursing students was compared with that isolated from blood culture specimens by arbitrarily primed (AP)-PCR analysis. The patterns obtained were different, a finding which excluded the presence of cross-infection. The present results show that basic preventive measures for cross-infection should be considered in the future, using such genetic analysis methods, so that MRCNS may not cause hospital infection.

Infection rates in surgical neonates and infants receiving parenteral nutrition: a five-year prospective study

We performed a prospective, observational, cohort study on 208 surgical neonates and infants between 1992 and 1997. Surveillance cultures of the oropharynx and rectum were obtained at the start of parenteral nutrition and thereafter twice weekly. Blood cultures were taken on clinical indication only. Microbial translocation was diagnosed when the micro-organisms in the blood were not distinguishable from those carried in the oropharynx and/or rectum. Liver function was monitored weekly and when septicaemia was suspected. The incidence of septicaemia was 15%. The predominant micro-organisms (86%) were the low-level pathogens, coagulase-negative staphylococci and enterococci. Potential pathogens, including aerobic Gram-negative bacilli, were responsible for the remainder. Microbial translocation was responsible for 84% of septicaemic episodes in 76% of patients. The potential pathogens caused septicaemia significantly later than coagulase-negative staphylococci, at a time when liver function was significantly more impaired. In neonates and infants receiving parenteral nutrition, septicaemia is mainly a gut-derived phenomenon and requires novel strategies for prevention.

Molecular epidemiology of coagulase-negative staphylococcal bacteraemia in a newborn intensive care unit

We isolated 55 coagulase-negative staphylococci (CoNS) over two separate 12-month periods (26 in 1993 and 29 in 1996) from the blood of neonates in a neonatal intensive case unit (NICU) in Melbourne, Australia and compared them by pulse-field gel electrophoresis profile (PFGE), random amplification of polymorphic DNA (RAPD) and antibiogram. The most common species were Staphylococcus epidermidis, S. haemolyticus and S. warneri. The majority of such isolates were resistant to penicillin and to either or both of methicillin and gentamicin. During 1993, there was an increase in the number of CoNS bloodstream infections compared with previous years. S. epidermidis was the most common isolate, with 88% assessed as clinically relevant. Using the three typing systems, we identified one likely epidemic clone of S. epidermidis, the isolates of which were resistant to penicillin, gentamicin and erythromycin and possessed the mecA gene. There was complete correlation between the detection of mecA and the phenotypic expression of resistance when zone diameters in the disc diffusion assay were interpreted according to the latest NCCLS guidelines (1999). Profiles of the remaining 1993 isolates were generally heterogeneous, suggesting independent acquisition with some evidence of cross-infection. The predominant bloodstream isolates in 1996 were heterogeneous multi-resistant strains of S. epidermidis, S. haemolyticus and S. warneri, about half of which were assessed as clinically relevant. These data support the view that CoNS are significant nosocomial pathogens in NICU and that resistant clones may be transmitted between babies. Molecular epidemiological tools are helpful for understanding transmission patterns and sources of infection, and are useful for measuring outcomes of intervention strategies implemented to reduce nosocomial CoNS sepsis. PFGE was found to be more discriminatory than RAPD, but the latter provides results in a more timely manner.

Frequency of low-level bacteremia in children from birth to fifteen years of age

A single blood culture inoculated with a small volume of blood is still frequently being used for the diagnosis of bacteremia in children because of the continued belief by many that bacteria are usually found in high concentrations in the blood of pediatric patients with sepsis. To determine the importance of both blood volume cultured and the number of culture devices required for the reliable detection of pathogens in our pediatric population, blood from children from birth to 15 years of age and with suspected bacteremia at York Hospital (a 500-bed community hospital) was inoculated into at least a Pediatric Isolator (Wampole Laboratories; 1.5 ml of blood) or a standard Isolator (10 ml of blood) and a bottle of ESP anaerobic broth (Trek Diagnostic Systems; 0.5 to 10 ml of blood). The use of a second Isolator and additional aerobic and anaerobic bottles and the total blood volume recommended for cultures (2 to 60 ml) depended on the weight and total blood volume of each patient. One hundred forty-seven pathogens were recovered from the blood of 137 (3.6%) of 3,829 children for whom culturing was done. Of 121 septic episodes for which the concentration of pathogens in the blood could be determined using Isolators, 73 (60. 3%) represented low-level bacteremia (</=10 CFU/ml of blood), including 28 pathogens (23.1%) which were detected at concentrations of only </=1.0 CFU/ml. Of 144 septic episodes for which two or more culture devices (Isolators and/or bottles) were inoculated, 85 (59%) were associated with false-negative results from one or more of the culture devices. Of the 128 children for whom antibiotic therapy records were complete, therapy was either started or changed for 88 (68.8%) following notification of positive blood cultures. Low-level bacteremia was common in our pediatric population, requiring the culturing of up to 4 or 4.5% of a patient's total blood volume for the reliable detection of pathogens and appropriate, timely changes in empiric therapy.

Antimicrobial resistance of coagulase-negative staphylococci from a Kuwait hospital

This study investigated the incidence of antimicrobial resistance in clinically significant coagulase-negative staphylococci at the Mubarak Al Kabeer Hospital, Kuwait. A total of 104 isolates of coagulase-negative staphylococci consisting of S. epidermidis (67), S. haemolyticus (16), S. saprophyticus (6), S. simulans (2), S. hominis (4), S. albus (2), S. sciuri (3), S. warneri (2), S. capitis (1), and S. xylosus (1) were isolated from clinical specimens over a 6-7 month period and tested for resistance to 22 antibacterial agents and the ability to produce slime. They were all susceptible to vancomycin and mupirocin but intermediate resistance to teicoplanin was detected in seven isolates: 83 and 47.7% were resistant to penicillin G and methicillin, respectively, 57% were resistant to gentamicin, 49.5% to erythromycin, 50.4% to tetracycline, and 52.3% to trimethoprim. Resistance to heavy metals and the nucleic-acid binding compound was also detected. More than half of S. epidermidis, S. saprophyticus, S. simulans, S. hominis, and all of S. haemolyticus were multiply resistant to three or more groups of antibiotics and there was a significant association between slime production and resistance to multiple antimicrobial agents in S. epidermidis. The results revealed a high level of resistance to commonly used agents.

Occurrence of nosocomial bloodstream infections in six neonatal intensive care units

BACKGROUND

Nosocomial bloodstream infections (NBSIs) occur frequently in neonatal intensive care units (NICUs) and are associated with substantial morbidity and mortality. Little has been published regarding variation in NBSI among institutions.

OBJECTIVE

To determine NBSI incidence among six NICUs and to explore how much variation is explained by patient characteristics and NICU practice patterns.

METHODS

From October, 1994, to June, 1996, six regional NICUs prospectively abstracted clinical records of all neonates weighing <1,500 g. Occurrence of NBSI, defined as first positive culture occurring >48 h after admission, was analyzed in relation to baseline patient characteristics and several common therapeutic interventions. Variables significant in univariate analyses were analyzed by Cox proportional hazards regression.

RESULTS

There were 258 NBSIs (incidence, 19.1%) among 1,354 inborn first admissions. Incidence varied significantly by site, from 8.5 to 42%. Birth weight, Broviac catheter use and parenteral nutrition were significantly associated with NBSI (P < 0.05). When controlling for these variables interinstitutional variation in NBSI occurrence decreased but remained significant.

CONCLUSIONS

Neonatal NBSI incidence varies substantially among institutions despite adjustment for length of stay and some known risk factors. The uses of Broviac catheters and especially intravenous nutrition supplements were significant determinants of NBSI risk.

Antibiotic susceptibility of staphylococci isolated in blood cultures in relation to antibiotic consumption in hospital wards

A total of 510 isolates of Micrococcaceae, 500 of staphylococci and 10 micrococci, detected in 485 (3.3%) of 14,860 consecutive blood cultures obtained from patients at a Swedish university hospital and 2 local hospitals were identified to species level and investigated for antibiotic susceptibility. The 5 most frequently isolated species were Staphylococcus epidermidis (54.8%), S. aureus (28.0%), S. hominis (3.4%), S. warneri (3.2%) and S. haemolyticus (2.8%). All isolates of S. aureus were oxacillin sensitive. Great diversity in antibiotic resistance among coagulase negative staphylococci between hospitals and different ward units in the university hospital was observed. The frequency of antimicrobial resistance among S. epidermidis correlated with the antibiotic consumption at different ward units, in particular for ciprofloxacin (p < 0.001) and co-trimoxazole (p < 0.004). The study emphasizes the importance of monitoring antibiotic consumption and resistance patterns of nosocomial staphylococci in order to avoid emergence and spread of multi-resistant bacteria within the hospital environment.

Phenotypic detection of nosocomial mecA-positive coagulase-negative staphylococci from neonates

Over a 3-year period, we screened antimicrobial resistance genotype (mecA-positive or -negative) in clinically significant coagulase-negative staphylococci isolated from patients residing in our neonatal intensive care unit. For the 152 study strains, the accuracy of standard methods (agar dilution MIC, disc diffusion and agar screen tests) in detecting oxacillin resistance during 48 h of incubation was evaluated. Using mecA gene PCR and Southern blot hybridization as the gold standard, the differential in MICs of additional antibiotics selected for their relevant clinical use in our setting was also compared with mecA status of the isolates. The frequency of mecA was 48.6% among study strains. When applying the previous (1998) and most current (1999) NCCLS interpretive criteria, the specificities of oxacillin agar dilution MICs in detecting the 78 mecA-negative isolates were 100 and 89.7%, respectively, at 24 h, and 100 and 80.7%, respectively, at 48 h. In this respect, the sensitivities of oxacillin agar dilution MICs in detecting the 74 mecA-positive strains were 75.6 and 97.2%, respectively, at 24 h, and 86.4 and 100%, respectively, at 48 h. When applying the previous and most current NCCLS zone size interpretive criteria, oxacillin zone diameters were in false-susceptible error for 13.5 and 8.1%, respectively, of the 74 mecA-positive strains tested at 24 h, and for 6.7 and 2.7%, respectively, at 48 h. Accordingly, when the 78 mecA-negative strains were considered, oxacillin zone diameters were in false-resistant error for 2.5 and 8.9%, respectively, at 24 h, and for 8.9 and 15.3%, respectively, at 48 h. The oxacillin salt agar screen assay accurately identified all mecA-negative strains at both 24 and 48 h. However, 26 (35.1%) and 7 (9.4%) of the mecA-positive strains were misinterpreted as susceptible by the agar screen test at 24 and 48 h, respectively. Using the presence of mecA as the reference standard for interpreting oxacillin susceptibility results, strains lacking mecA were more likely to be susceptible to ampicillin, ceftazidime, gentamicin, netilmicin and rifampicin than were mecA-positive strains. Vancomycin was the only antibiotic tested for which all strains, regardless of mecA status, remained susceptible.

C-reactive protein (CRP) response patterns in neonatal septicaemia

C-reactive protein (CRP) is an unreliable diagnostic tool in the early diagnosis of neonatal septicaemia. However, serial measurements have been shown to be useful in monitoring the effectiveness of treatment. The aim of the present study was to investigate whether a specific CRP response pattern to different groups of pathogens could be identified during treatment of neonatal septicaemia. Serial CRP measurements from day 1 to 4 in monomicrobial blood culture-proven episodes of septicaemia were reviewed. In 4416 admissions, 180 out of 206 positive blood cultures were monomicrobial; 121 monomicrobial septic episodes were eligible for final analysis of the CRP response during treatment. A low median (M) value (day 1 to 4) was identified in coagulase-negative staphylococci (CONS) (M=23 mg/l), contrasting with high median values in Staphylococcus aureus (M=58 mg/l), group B streptococci (M=51 mg/l), Escherichia coli (M=51 mg/l) and Candida species (M=76 mg/l) (p<0.001). Median CRP values in the two groups were different for each of the treatment days 1 to 4 (p<0.001). An increase (p<0.001) in CRP during the 24 h before initiation of treatment was a sign of late-onset CONS septicaemia. In episodes where antimicrobial treatment failed, CRP levels were moderately elevated the day prior to treatment start and increased continuously thereafter, whereas successful treatment was generally accompanied by a decline in CRP in less than 4 days. The CRP response to CONS is significantly less pronounced than to other commonly encountered pathogens in neonatal septicaemia. A rise in CRP beyond the third day of empirical treatment should give rise to a suspicion of fungal infection or ineffective antibacterial treatment.

Impact of the high-affinity proline permease gene (putP) on the virulence of Staphylococcus aureus in experimental endocarditis

Staphylococcus aureus causes a wide variety of invasive human infections. However, delineation of the genes which are essential for the in vivo survival of this pathogen has not been accomplished to date. Using signature tag mutagenesis techniques and large mutant pool screens, previous investigators identified several major gene classes as candidate essential gene loci for in vivo survival; these include genes for amino acid transporters, oligopeptide transporters, and lantibiotic synthesis (W. R. Schwan, S. N. Coulter, E. Y. W. Ng, M. H. Langhorne, H. D. Ritchie, L. L. Brody, S. Westbrock-Wadman, A. S. Bayer, K. R. Folger, and C. K. Stover, Infect. Immun. 66:567-572, 1998). In this study, we directly compared the virulence of four such isogenic signature tag mutants with that of the parental strain (RN6390) by using a prototypical model of invasive S. aureus infection, experimental endocarditis (IE). The oligonucleotide signature tag (OST) mutant with insertional inactivation of the gene (putP) which encodes the high-affinity transporter for proline uptake exhibited significantly reduced virulence in the IE model across three challenge inocula (10(4) to 10(6) CFU) in terms of achievable intravegetation densities (P, <0.05). The negative impact of putP inactivation on in vivo survival in the IE model was confirmed by simultaneous challenge with the original putP mutant and the parental strain as well as by challenge with a putP mutant in which this genetic inactivation was transduced into a distinct parental strain (S6C). In contrast, inactivation of loci encoding an oligopeptide transporter, a purine repressor, and lantibiotic biosynthesis had no substantial impact on the capacity of OST mutants to survive within IE vegetations. Thus, genes encoding the uptake of essential amino acids may well represent novel targets for new drug development. These data also confirm the utility of the OST technique as an important screening methodology for identifying candidate genes as requisite loci for the in vivo survival of S. aureus.

Evaluation of the microbiology of chronic maxillary sinusitis

Chronic paranasal sinusitis is a disease that afflicts a significant percentage of the population and causes considerable long-term morbidity. With the common use of multiple courses of broad-spectrum oral antibiotics to treat this condition, there is a possibility of an alteration in the pathogens that promote a persistence of chronic sinusitis. One hundred seventy-four consecutive patients with a diagnosis of chronic maxillary sinusitis requiring an endoscopic surgical procedure were prospectively evaluated. At the time of surgery, cultures of mucopus in the maxillary sinus were aseptically obtained endoscopically and cultured for aerobes, anaerobes, and fungus. Two hundred seventeen isolates from 174 patients were obtained. Coagulase-negative staphylococci were the most common isolates (36%), followed by Staphylococcus aureus (25%), Streptococcus viridans (8.3%), Corynebacterium (4.6%), and anaerobes (6.4%). Although coagulase-negative Staphylococcus is not considered a pathogen, of the 24 isolates that had sensitivity testing performed, 13 demonstrated resistance to multiple antibiotics, including cephalothin, erythromycin, oxacillin, sulfonamides, and clindamycin. This study demonstrates that aerobic rather than anaerobic bacteria are the more common pathogens in chronic sinusitis. In addition, coagulase-negative Staphylococcus may be a pathogen in the disease process, and sensitivities should be obtained of this isolate for evaluation and possible treatment.

Antimicrobial resistance in bacterial chronic sinusitis

Recent reports describe the emergence of antimicrobial resistant bacteria in acute sinusitis and an increased incidence of enteric gram negative bacilli in chronic sinusitis. The objective of this cross sectional study is to identify the emergent resistance patterns in bacterial chronic sinusitis. Specifically, this article seeks to characterize the bacteriology of outpatient chronic sinusitis, then to compare the antimicrobial susceptibilities of the bacterial isolates with standard culture data from a tertiary care center. Between March and August, 1994, 113 new outpatients presented with chronic sinusitis at a major teaching institution. Of these patients 34 underwent endoscopically guided aerobic culture of the paranasal sinuses and nasal cavities. Of the 48 total cultures, there were 43 positive cultures yielding 72 isolates. Thirty-eight cultures had two or fewer isolates; four cultures had three plus isolates, and one culture grew out normal flora. The most frequently isolated organisms were coagulase negative Staphylococcus (SCN), 20 (28%); Pseudomonas aeruginosa, 12 (17%); and Staphylococcus aureus, 9 (13%). Within the limited sample size for each isolate, Staphylococcus coagulase negative, Pseudomonas, and Pneumococcus demonstrated higher antimicrobial resistance compared to the medical center's corresponding nonurinary isolates. Additionally, three of six patients with Pseudomonal aeruginosa (50%) had a quinolone resistant strain. These preliminary data suggest that both an increased incidence of antimicrobial resistance and of enteric gram negative bacilli may exist in these outpatient, tertiary care center patients with chronic bacterial sinusitis.

Efficacy of trovafloxacin, a new quinolone antibiotic, in experimental staphylococcal endocarditis due to oxacillin-resistant strains

Therapeutic options for severe infections caused by strains of oxacillin-resistant Staphylococcus aureus (ORSA) and coagulase-negative staphylococci (ORSE) are very limited. With the increasing resistance of such strains to aminoglycosides, rifampin, and currently available quinolone agents, as well as the recent documentation of increasing resistance of ORSA to vancomycin (VANCO), new treatment alternatives are imperative. The in vivo efficacy of trovafloxacin (TROVA), a new quinolone agent with excellent antistaphylococcal activity in vitro, against experimental endocarditis (IE) due to beta-lactamase-producing ORSA and ORSE strains (ORSA and ORSE IE) was evaluated. TROVA (25 mg/kg of body weight intravenously [i.v.] twice daily [b.i.d]) was compared to VANCO (20 mg/kg i.v. b.i.d.) and two regimens of ampicillin-sulbactam (AMP-SUL; 200 mg/kg intramuscularly [i.m.] three times a day [t.i.d.] and 20 mg/kg i.m. b.i.d.), with all agents given for 3 or 6 days. AMP-SUL was included as a comparative treatment regimen because of its proven efficacy against experimental ORSA and ORSE IE. For both ORSA and ORSE IE, TROVA, AMP-SUL, and VANCO each reduced staphylococcal densities in vegetations compared to untreated controls (P < 0.01). For ORSA IE, TROVA was the most rapidly bactericidal agent--although not to a statistically significant degree--correlating with its superior bactericidal effect in vitro compared to those of VANCO and AMP-SUL.

Intravenous lipid emulsions are the major determinant of coagulase-negative staphylococcal bacteremia in very low birth weight newborns

BACKGROUND

Intravenous lipid emulsions and the i.v. catheters through which they were administered were the major risk factors for nosocomial coagulase-negative staphylococcal (CONS) bacteremia among newborns in our neonatal intensive care units a decade ago. However, medical practice is changing, and these and other interventions may have different effects in the current setting.

OBJECTIVES

We determined the independent risk factors for CONS bacteremia in current very low birth weight newborns after adjusting for severity of underlying illness.

METHODS

We surveyed 590 consecutively admitted newborns with birth weights < 1500 g hospitalized in 2 neonatal intensive care units and conducted a case-control study in a sample of 74 cases of CONS bacteremia and 74 pairs of matched controls. Adjusted relative odds of bacteremia were estimated for a number of attributes and therapeutic interventions in 2 time intervals before CONS bacteremia: any time before bacteremia and the week before bacteremia.

RESULTS

Using conditional logistic regression to adjust for indicators of severity of illness, two procedures were independently associated with subsequent risk of CONS bacteremia at any time during hospitalization: i.v. lipids, odds ratio (OR) = 9.4 [95% confidence interval (CI) 1.2 to 74.2]; and any surgical or percutaneously placed central venous catheter, OR = 2.0 (95% CI 1.1 to 3.9). Considering only the week immediately preceding bacteremia, the independent risk factors were: mechanical ventilation, OR = 3.2 (95% CI 1.3 to 7.6); and short peripheral venous catheters, OR = 2.6 (95% CI 1.0 to 6.5).

CONCLUSIONS

During the last decade exposure to i.v. lipids any time during hospitalization has become an even more important risk factor for CONS bacteremia (OR = 9.4). Of these bacteremias 85% are now attributable to lipid therapy. In contrast the relative importance of intravenous catheters as independent risk factors has declined. Mechanical ventilation in the week before bacteremia has emerged as a risk factor for bacteremia.

Antimicrobial resistance in staphylococci. Epidemiology, molecular mechanisms, and clinical relevance

Staphylococcal infections continue to pose important clinical problems in children and adults. Antibiotic resistance among the staphylococci has rendered therapy of these infections a therapeutic challenge. Despite early, uniform susceptibility to penicillin, staphylococci acquired a gene elaborating beta-lactamase that rendered penicillin inactive and that is borne by nearly all clinical isolates. "Penicillinase-resistant beta-lactams," such as methicillin, were introduced in the early 1960s, but resistance to them has become an increasing concern. The mechanism of the so-called "methicillin resistance" is complex. Moreover, once confined to the ecology of hospitals and other institutions, a recent increase in community-acquired methicillin-resistant S. aureus infections has been observed. Glycopeptides, until now the only uniformly reliable therapeutic modality, have been increasingly used for therapy of staphylococcal infections. The recent recognition of clinical isolates with reduced susceptibility to glycopeptides is of concern.

Frequency of low level bacteremia in infants from birth to two months of age

BACKGROUND

The frequency of low level bacteremia (< or = 10 colony-forming units/ml) in infants from birth to 2 months of age and the optimal volume of blood and number of blood cultures to be collected have not been well-documented. During 1991 guidelines at this hospital for collection of blood for culture from these infants were revised.

METHODS

Blood from each infant with suspected bacteremia was usually inoculated into an Isolator 1.5 Microbial Tube (1.5 ml of blood) and a bottle of anaerobic broth (0.5 to 3.0 ml of blood). The use of a second Isolator tube and the total blood volume recommended for culture (2 to 6 ml) depended on the weight and total blood volume of each infant.

RESULTS

Forty-four bacterial pathogens were recovered from the blood of 40 (2.5%) of 1589 infants. Of 34 infants from whose blood the concentration of pathogens could be determined, 23 (68%) had low level bacteremia. Of 50 isolates of pathogens recovered from Isolator cultures, 32 (64%) were detected in counts of < or = 10 colony-forming units/ml. When 2 or 3 blood culture devices were inoculated with a total of 2 to 6 ml of blood from each infant, significantly more cases of bacteremia were detected (34 (3.0%) of 1126 infants had positive blood cultures) than when only one culture device containing < or = 1.5 ml of blood was used (2 (0.5%) of 398 infants had positive blood cultures; P = 0.008). However, when 4 or more culture devices were inoculated with a total of > 6 ml of blood from each infant (5 (7.7%) of 65 infants had positive blood cultures), the difference in recovery of pathogens compared with the culturing of from 2 to 6 ml of blood per infant was not significant (P = 0.089).

CONCLUSIONS

Low level bacteremia was common in our infants' patient population. The culturing of up to 6 ml of blood which represented up to 4.5% of an infant's total blood volume was required for detection of the pathogens.

Topical ointment therapy benefits premature infants

OBJECTIVE

Premature infants have an ineffective epidermal barrier. The aim of this study was to investigate the cutaneous and systemic effects of preservative-free topical ointment therapy in premature infants.

STUDY DESIGN

We conducted a prospective, randomized study of 60 infants less than 33 weeks' estimated gestational age. The treated infants received therapy for 2 weeks with twice-daily preservative-free topical ointment therapy while the control group received no topical treatment or as-needed therapy with a water-in-oil emollient. Data collection included transepidermal water loss (TEWL) measurement, skin condition evaluations, fungal and quantitative bacterial skin cultures, analysis of fluid requirements, patterns of weight low or gain, and the incidence of blood and cerebrospinal fluid cultures positive for microorganisms.

RESULTS

We found that topical ointment therapy significantly decreased TEWL during the first 6 hours after the initial application. TEWL was decreased by 67% (p = 0.0001) when measured 30 minutes after application and 34% (p = 0.001) when measured 4 to 6 hours after application. We also observed significantly superior skin condition scores in the treated group on study days 7 and 14 (p = 0.001) and 0.0004, respectively). Quantitative bacterial cultures revealed significantly less colonization of the axilla on day 2, 3, or 4 and on day 14 (p = 0.008 and 0.04, respectively). The incidence of positive findings in blood and/or cerebrospinal fluid cultures was 3.3% in the treated group of infants versus 26.7% in the control group (p = 0.02). There was no statistical difference in the fluid requirements or patterns of weight gain or loss during the 2 weeks of the study.

CONCLUSIONS

Preservative-free topical ointment therapy decreased TEWL for 6 hours after application, decreased the severity of dermatitis, and decreased bacterial colonization of axillary skin. Infants treated with ointment had fewer blood and cerebrospinal fluid cultures positive for microorganisms. These data support the use of topical ointment therapy in very premature infants during the first weeks after birth.

Coagulase-negative Staphylococci in Danish blood cultures: species distribution and antibiotic susceptibility

The distribution and antibiotic susceptibility of coagulase-negative staphylococci (CoNS) isolated from blood cultures was examined in samples from hospitals covering most of Denmark. A total of 499 CoNS isolates were detected in 477 blood cultures from 340 patients and speciated as Staphylococcus epidermidis, 285; Staphylococcus hominis, 61; Staphylococcus haemolyticus, 43; Staphylococcus warneri, 12; Staphylococcus cohnii, 7; Staphylococcus saprophyticus, 4; Staphylococcus capitis, 2 and Staphylococcus lugdunensis, 1. Seventy-eight isolates could not be identified to species level and six were Micrococcus spp. In 108 (22.6%) blood culture sets, more than one CoNS strain were found, as detected by species identification, antibiogram and biotyping. Significantly more blood cultures from patients in university hospitals were drawn from central venous catheters. Comparing university and non-university hospitals, the overall antibiotic susceptibility among CoNS was only slightly different, except for methicillin and amikacin. The prevalence of methicillin-resistant strains was 35.1% in the university hospital strains vs. 25.3% in the non-university hospital strains. The overall prevalence of methicillin resistance was 32%. Great geographic variation in both species distribution and antibiotic resistance was observed. The high prevalence of S. epidermidis makes subtyping of this species important.

Ampicillin-sulbactam is effective in prevention and therapy of experimental endocarditis caused by beta-lactamase-producing coagulase-negative staphylococci

Optimal strategies for the prophylaxis and therapy of endocarditis caused by oxacillin-resistant, coagulase-negative staphylococci in patients with native or prosthetic valvular heart disease are not well defined. We compared the in vivo efficacies of ampicillin-sulbactam-based regimens with those of vancomycin-based oxacillin-resistant, beta-lactamase-producing coagulase-negative staphylococcal isolate (Staphylococcus haemolyticus SE220). Ampicillin-sulbactam (100 and 20 mg/kg of body weight, respectively, given intramuscularly in a two-dose regimen) was equivalent to vancomycin (30 mg/kg given intravenously in a two-dose regimen) in its prophylactic efficacy against the coagulase-negative staphylococcal strain (93 and 80%, respectively). The combination of ampicillin-sulbactam plus either rifampin or vancomycin did not enhance the prophylactic efficacy compared with that of ampicillin-sulbactam or vancomycin alone. In the therapy of established aortic valve endocarditis in rabbits caused by this same coagulase-negative staphylococcal strain, animals received 7-day ampicillin-sulbactam-based or vancomycin-based regimens with or without rifampin. All treatment regimens were effective at lowering intravegetation coagulase-negative staphylococcal densities and rendering vegetations culture negative compared with the coagulase-negative staphylococcal densities and vegetations of untreated controls, with ampicillin-sulbactam in combination with rifampin or vancomycin being the most active regimen. However, only the regimen of ampicillin-sulbactam in combination with vancomycin effectively prevented relapse of endocarditis posttherapy after a 5-day antibiotic-free period. For animals receiving rifampin-containing regimens, relapses of endocarditis were associated with the in vivo development of rifampin resistance among coagulase-negative staphylococcal isolates in the vegetation. Ampicillin-sulbactam was highly effective in the prevention of experimental endocarditis caused by a beta-lactamase-producing, oxacillin-resistant coagulase-negative staphylococcal strain. Ampicillin-sulbactam was also efficacious for the therapy of coagulase-negative staphylococcal endocarditis, especially when it was combined with vancomycin to prevent posttherapeutic relapses.

Cross infections due to coagulase-negative staphylococci in high-risk patients

Until recently, infections due to coagulase-negative staphylococci (CNS) have been regarded as endogenous in origin. However, there are now increasingly reports in the literature on the endemic occurrence of distinct strains of CNS. Several outbreaks due to CNS are reported in cardiac surgery or in neonates. The latter seem to be high risk populations in regard to CNS infections because of certain risk factors (i.e. degree of immunosupression, routine use of central venous catheters and parenteral lipids as well as broad spectrum antibiotic therapy). On the other hand, these newborn babies have no physiological skin flora and are therefore easily colonized by multiresistent bacteria. The persistence of certain well-defined Staphylococcus epidermidis (SE) strains in neonatal intensive care units have been demonstrated over periods as long as a decade. Specific putative virulence factors (i.e. slime production and polysaccharide/adhesin PS/A) were more common in endemic strains as compared to single isolates. Pulsed-field gel electrophoresis (PFGE) proves to be a powerful tool in the study of the epidemiology of CNS while other modern typing techniques (ribotyping, plasmid typing) were also used in the literature to investigate outbreaks of CNS infections.

Molecular epidemiology of Staphylococcus epidermidis blood isolates from neonatal intensive care unit patients

Twelve episodes of Staphylococcus epidermidis bacteraemia occurred within three months in a neonatal intensive care unit. Plasmid profiles and Southern blot hybridization with five different probes were used to determine whether an endemic strain of S. epidermidis could be identified among the contemporary isolates. It was concluded that this methodology was satisfactory for differentiation between isolates of coagulase-negative staphylococci: fifteen isolates were divided in eight groups indicating that there was no single endemic strain causing the outbreak.

Antimicrobial resistance in staphylococci

Staphylococci have developed a variety of strategies for dealing with the presence of antibiotics encountered in clinical environments. Resistance to beta-lactams and other antimicrobial agents has been accomplished by a diverse array of molecular mechanisms. Options available to treat infections caused by staphylococci resistant to methicillin are limited, and the next generation of antibiotics to be introduced, should glycopeptide resistance become an important clinical problem, is not yet on the horizon.

Evaluation of staphylococci isolated from a blood culture system (Colorbact)

During a one-year period, all blood cultures positive for staphylococci from two of the smaller Danish counties with non-university hospitals only were evaluated. The isolates were speciated and coagulase-negative staphylococci (CoNS) were biotyped. Furthermore, antibiogram, phage typing and lectin typing were performed for all isolates. Clinical information was obtained by telephone, and before any bacteriological identification was performed, a preliminary judgment was made as to whether the positive blood culture was of clinical significance. A total of 3,500 blood cultures were evaluated and 426 (12.2%) were positive. One hundred and sixty blood cultures from 137 patients contained staphylococci; 36 of these patients had a pure culture of Staphylococcus aureus. One hundred and twenty-four CoNS were found and identified as S. epidermidis (81), S. hominis (19), S. haemolyticus (8), S. simulans (1), and Micrococcus species (3), and another 12 staphylococcal isolates which could not be identified to species level. A total of 35 patients had mixed cultures, including 6 with S. aureus as one of the isolates and 15 with mixed CoNS. Clinical relevance was estimated in 90% of cases where the later bacterial identification showed S. aureus, whereas clinical relevance was absent in the majority of cases including CoNS. Methicillin and gentamicin resistance was absent among S. aureus, but frequent among CoNS, especially S. epidermidis, where 40% were resistant to methicillin and 30% to gentamicin.

Update on clinical significance of coagulase-negative staphylococci

The clinical significance of coagulase-negative Staphylococcus species (CNS) continues to increase as strategies in medical practice lead to more invasive procedures. Hospitalized patients that are immunocompromised and/or suffering from chronic diseases are the most vulnerable to infection. Since CNS are widespread on the human body and are capable of producing very large populations, distinguishing the etiologic agent(s) from contaminating flora is a serious challenge. For this reason, culture identification should proceed to the species and strain levels. A much stronger case can be made for the identification of a CNS etiologic agent if the same strain is repeatedly isolated from a series of specimens as opposed to the isolation of different strains of one or more species. Strain identity initially can be based on colony morphology, and then one or more molecular approaches can be used to gain information on the genotype. Many of the CNS species are commonly resistant to antibiotics that are being indicated for staphylococcal infections, with the exception of vancomycin. The widespread use of antibiotics in hospitals has provided a reservoir of antibiotic-resistant genes. The main focus on mechanisms of pathogenesis has been with foreign body infections and the role of specific adhesins and slime produced by Staphylococcus epidermidis. Slime can reduce the immune response and opsonophagocytosis, thereby interfering with host defense mechanisms. As we become more aware of the various strategies used by CNS, we will be in a better position to compromise their defense mechanisms and improve treatment.

Clinical index to predict bacteraemia caused by staphylococci

OBJECTIVES

To define risk factors associated with bacteraemia caused by Staphylococcus aureus or coagulase-negative staphylococci; and to use them to define patients in need of empiric anti-staphylococcal antibiotic treatment.

DESIGN

Derivation set: observational, prospective study; validation set: retrospective analysis of a prospectively collected database.

SETTING

Derivation set: Beilinson Medical Centre, Petah Tiqva, Israel--a 900-bed university hospital. Validation set: St Thomas's Hospital, London, UK--an 800-bed teaching hospital.

SUBJECTS

All episodes of bacteraemia detected at Beilinson Medical Centre between March 1988 and September 1990 (derivation set, n = 1410), and at St Thomas's Hospital during 1987-1990 (validation set, n = 1040).

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

Percentage of staphylococcal bacteraemia in groups of patients defined by the models.

RESULTS

The following factors were associated with Staphylococcus aureus bacteraemia: focus of infection (whether high or low risk), haemodialysis, intravenous drug abuse and infection acquired in the orthopaedic ward. A logistic model was used to divide the derivation set into three groups with percentages of Staphylococcus aureus bacteraemia of 1.8%, 13.2% and 33.7% (P < 0.0001); and the validation group 2.5%, 18.2% and 53.2% (P < 0.0001). Factors associated with coagulase-negative staphylococcal bacteraemia were: central or peripheral intravenous catheter as the focus of infection, a preterm neonate, the presence of a central intravenous catheter, low temperature, and a low white blood cell count. A second model including those factors was used to divide the derivation set into three groups with percentages of coagulase-negative staphylococcal bacteraemia of 1.9%, 22.8%, and 43% (P < 0.0001). In the validation set, the percentages were 2.9%, 22.4% and 31.0% (P < 0.001).

CONCLUSIONS

The present study defines groups at high risk for staphylococcal bloodstream infection, in which empiric treatment should include an anti-staphylococcal drug.

Central line perforation associated with Staphylococcus epidermidis infection

We present detailed case reviews of four very low birth weight (VLBW) infants in whom central venous silastic catheter perforation was associated with Staphylococcus epidermidis sepsis. The diagnostic and therapeutic dilemma presented by the intracavitary fluid collections occurring in all four of these cases proved to be of clinical interest. Additionally, we propose a model that may account for the etiology of catheter displacement--localized phlebitis as a result of S epidermidis infection with resultant extralumenal migration of the central venous catheter.

Species distribution of coagulase-negative staphylococcal isolates at a community hospital and implications for selection of staphylococcal identification procedures

A total of 499 coagulase-negative staphylococci (CoNS) were isolated from a variety of clinical specimens at a community hospital. Ten different species and many strains of CoNS were identified. Staphylococcus epidermidis was the most common isolate. The species distribution suggests that S. saprophyticus and, to a lesser extent, S. haemolyticus may be important in urinary tract infections. S. lugdunensis may be a significant isolate from wound infections. Frequently, mixed cultures were found with either multiple species or multiple strains of the same species of CoNS. These mixed cultures could not be detected by colony morphology upon initial overnight incubation of the cultures but could be distinguished following colony development for several days. In addition, sequential positive cultures from an individual patient often yielded different species or different strains of the same species which again could not be detected upon initial observations of colony morphology. Procedures for the identification of the CoNS need to be improved, and microbiology laboratories should consider the use of more definitive identification procedures for the CoNS.

A study of the epidemiology of an endemic strain of staphylococcus haemolyticus (TOR-35) in a neonatal intensive care unit

Coagulase-negative staphylococci (CNS) are among the most prevalent microorganisms that colonize and cause sepsis in neonatal intensive care units (NICU). We had previously identified a strain of CNS, Staphylococcus haemolyticus (TOR-35), in the NICU at Mount Sinai Hospital, that had been repeatedly isolated from blood cultures from neonates. We therefore carried out a prospective study to determine the frequency and time of colonization and the frequency of bacteremia in neonates over a 3.5 month period. This was accomplished by obtaining surface swabs within 1 h of birth and on days 3, 5, and 7 and by characterizing all blood culture isolates of CNS. We also determined what percentage of neonatal CNS bacteremias were due to this strain, between January 1, 1987 and December 31, 1990, by retrieving and typing all stock cultures of CNS from that period. All isolates were typed by species identification and antimicrobial susceptibility profile code. There were 76 (38%) neonates that became colonized with the TOR-35 strain at some time during their NICU stay. Lower birth weight was associated with colonization (p < 0.001), as was lower gestational age (p < 0.001). Only 1 neonate had a positive blood culture isolate for the TOR-35 strain during the prospective study. Of the 4 years of neonatal bacteremias that were studied retrospectively, there were 252 episodes of CNS bacteremia, of which 27 (11%) were due to the TOR-35 strain. The TOR-35 strain has become endemic in our NICU and appears to selectively colonize premature, low birth weight newborn infants, but only infrequently causes bacteremia.

An analysis of the microbial flora of premature neonates

An analysis of the microbial flora of 10 premature neonates hospitalized in a neonatal intensive care unit (NICU) was made. The babies had received neither antibiotics nor antiseptics and nine out of 10 were born by caesarean section. Samples were collected on the fourth or fifth day of life from 18 skin or mucosal sites. Detailed bacterial counts were obtained by plating out suitable dilutions of the samples on to selective media. Representative samples of each colony type were then subcultured and identified, using standard laboratory methods. Two hundred and fifty-six isolates of staphylococci were obtained and their susceptibility to 23 antibiotics tested. Only 11% of the samples were sterile. Coagulase-negative staphylococci (CNS) were the commonest species isolated and were predominant in every site studied. They were found in 79% of the samples and represented almost 81% of the neonates' flora. Eight species and biotypes of CNS were identified. In decreasing order of frequency, they comprised S. epidermidis (biotypes 1 and 2), S. hominis (biotype 1), S. warneri, S. haemolyticus, S. capitis, S. cohnii and S. hominis (biotype 2). CNS distribution appeared to be highly heterogeneous with no significant specificity of any species for a particular body site. The main quantitative and qualitative variations seemed to relate to the method of delivery, and the intensity and nature of exposure of the neonate to its local environment. A high level of antibiotic resistance was found among the CNS isolates (especially S. epidermidis and S. haemolyticus): penicillin G (96%), oxacillin (31%), erythromycin (52%) and gentamicin (28%). Moreover, multiresistant strains were numerous, supporting the nosocomial origin of CNS.

Clinical significance of Staphylococcus warneri bacteremia

Twenty-seven episodes of bacteremia caused by Staphylococcus warneri were identified at Long Island Jewish Medical Center in New York between 1984 and 1989. Fourteen of these were thought to represent true bacteremias and 13 to represent contaminants. Of the 14 true bacteremias, 5 were in pediatric and 9 were in adult patients. Eight of 14 patients (57%) had catheter-related bacteremia and 5 of 14 had bacteremia of unknown source. There was one case of fulminant native valve S. warneri endocarditis. All cases of catheter-related bacteremia, except one, were nosocomially acquired, and 75% of these patients had an underlying immunosuppressive condition. Only 40% of patients with bacteremias of unknown source were immunocompromised, and S. warneri appeared to be noninvasive in this group. Interestingly, all five of the pediatric isolates were oxacillin susceptible, although four of five were resistant to penicillin, despite the fact these patients were hospitalized an average of 29 days. In contrast, seven of nine adult isolates were resistant to both oxacillin and penicillin. The only case of native valve S. warneri endocarditis occurred in a patient who had no known underlying valvular heart disease, but had an underlying immunosuppressive condition. Identification to species level of coagulase-negative staphylococci may lead to appreciation of the importance of bacteria such as S. warneri as human pathogens.

Comparison of blood cultures with corresponding venipuncture site cultures of specimens from hospitalized premature neonates

We compared the presence and identities of isolates from blood culture samples obtained by percutaneous venipuncture with those of commensal skin organisms cultured from respective venipuncture sites after skin cleansing; 677 blood and skin site culture pairs from 488 infants were compared. Organisms grew in 58 blood cultures; nine of these cultures had corresponding venipuncture site cultures that also grew organisms. Forty-two blood culture isolates were coagulase-negative staphylococci; five of these were associated with similar venipuncture site cultures. According to restriction-endonuclease fingerprinting of chromosomal DNA and plasmid analysis, three pairs of blood and venipuncture site cultures were identical and two pairs were different. Thus only 7% (3/42) of coagulase-negative staphylococcal blood isolates were associated with identical contamination at the venipuncture site. We conclude that, if the venipuncture site has been carefully cleansed, the growth of coagulase-negative staphylococci in blood cultures of specimens from premature neonates indicates bacteremia rather than skin contamination in the vast majority of cases.

The impact of converting to a biphasic blood-culture system on the overall cost and the incidence of pseudobacteremia

After converting from a conventional broth (CB) system to a biphasic (BP) agar-slide blood-culture system (Septi-Chek), our laboratory noted an increase in positive blood cultures in general, and in coagulase-negative staphylococci (CNS) in particular. To investigate these findings, we compared all blood cultures collected over a 21-month period using CB and then BP systems, totaling 28,199 blood cultures. The frequency of positive blood cultures increased from 9.2% to 12.7% (p less than 0.0001), whereas CNS isolation increased from 2.6% to 5.2% (p less than 0.0001). There was no significant change in the incidence of true primary or secondary bacteremia due to CNS (p = 0.9). The isolation of other pathogens, including Staphylococcus aureus, Candida albicans, Bacteroides species, and Gram-negative bacilli increased from 6.5% to 7.1% (p less than 0.05). We estimated the cost of processing 28,000 blood cultures by both CB and BP systems, using positivity rates of 9.2% and 12.7%, respectively, and standards provided by the College of American Pathologists (CAP, 1991) for workload hours of technologist time. We calculated a higher overall cost for the BP system. However, the use of this system eliminated the use of needles and syringes for subculture of bottles showing no growth, thus decreasing the risk of technologist exposure to body fluids. Despite the increased cost and more frequent occurrence of pseudobacteremia, the enhanced sensitivity and increased safety of the BP system justified its use in the prompt identification of patients with true bacteremia.

Bacteraemia in man and animals: an overview

Bacteraemia signifies invasion of the bloodstream by bacteria. In most systemic infections in man and animals, bacteria enter the blood at some stage during the infection and are rapidly distributed throughout the body. A wide variety of organisms have been associated with bacteraemia. Prompt detection of the aetiological agents of bacteraemia is of prime importance in clinical microbiology. There are no defined recommendations for blood cultures in animals but both conventional and improved methods are available for detection of bacteraemia in man. The consequences of bacteraemia are as diverse as the potential aetiological agents. Monoclonal antibodies to the core glycolipid (lipid A) seems very promising for the treatment of bacteraemia and septic shock caused by Gram-negative bacteria in man and animals.

Typing of multiple isolates of coagulase-negative staphylococci from blood cultures and cerebrospinal fluid in neonates and children: an approach to discriminate contaminants

From eight neonates and children suspicious for suffering from septicemia and/or meningitis, coagulase negative staphylococci (CNS) were isolated from multiple blood cultures and from cerebrospinal fluids originating from different punctures. S. epidermidis was the predominant species. By a further typing using plasmid-profiles and exoprotein patterns besides the resistance phenotype, contaminants could be discriminated from the isolates as the probable etiologic agent exhibiting unique reaction patterns. CNS isolated from cases of septicemia together with other bacterial pathogens or from cases of presumed but not confirmed septicemia revealed as different.

Association of intravenous lipid emulsion and coagulase-negative staphylococcal bacteremia in neonatal intensive care units

BACKGROUND AND METHODS

Coagulase-negative staphylococci are now the chief cause of bacteremia in neonatal intensive care units. To investigate potential risk factors for this nosocomial infection, we conducted a case--control study among 882 infants treated in two neonatal intensive care units during 1982.

RESULTS

The 38 case patients and 76 controls were similar with respect to 27 indicators of the severity of the underlying illness. In addition, of the 20 potential risk factors for bacteremia that we investigated, only 2 met conventional criteria for causality. Infants with coagulase-negative staphylococcal bacteremia were 5.8 times as likely as controls (95 percent confidence interval, 4.1 to 8.3) to have received intravenous lipid emulsion before the onset of bacteremia. Because the use of lipids was common, 56.6 percent of all of the cases of nosocomial bacteremia could be attributed to lipid administration. Infants with bacteremia were also 3.5 times as likely as controls (95 percent confidence interval, 1.4 to 8.3) to have had a percutaneously inserted central venous catheter (attributable risk, 14.9 percent). The induction time for bacteremia after lipid administration, usually through peripheral catheters, was often less than one day. In contrast, the average induction period for nosocomial bacteremia associated with the use of central catheters, which were rarely used for lipid administration, was at least 5.5 days. Similar analyses of data on an additional 31 neonates treated in 1988 confirmed the strong and apparently independent association of coagulase-negative staphylococcal bacteremia with the intravenous administration of lipids (adjusted odds ratio, 5.3; 95 percent confidence interval, 3.5 to 6.7).

CONCLUSIONS

The risk of coagulase-negative staphylococcal bacteremia in infants in neonatal intensive care units can be attributed primarily to the intravenous administration of lipid emulsions. Since lipids are critical for the nutritional support of premature infants, further studies are needed to examine the pathogenesis and prevention of lipid-associated bacteremia.

Coagulase-negative staphylococci: incidence, pathogenicity, and treatment in the 1990s

Coagulase-negative staphylococci (CNS), which historically have been viewed as contaminants when recovered in culture media, are now recognized as opportunistic pathogens of increasing importance in hospital-acquired infections. They are frequently found colonizing prosthetic devices and intravenous lines. CNS are capable of producing a variety of infections including deep-seated infections such as endocarditis and meningitis. Staphylococcus epidermidis is the most commonly isolated CNS and it appears to be the most resistant to antibiotics, making antimicrobial therapy challenging. Treatment of the infection will very often require removal of a prosthetic device, if present. An adequate infection control program is imperative in prophylaxis against this infection.

Coagulase-negative staphylococci: interplay of epidemiology and bench research

Coagulase-negative staphylococci (CNS) are major nosocomial pathogens in patients with prostheses and indwelling devices such as central venous catheters. For Staphylococcus epidermidis the unique association with foreign-body infections appears to be due in part to a capsular polysaccharide adhesin that mediates attachment to silicon elastomer and other biomedical materials. In addition, staphylococcal "slime" may promote persistent colonization of indwelling devices and protect staphylococci from clearance by host defense mechanisms. Given these research findings, it seemed reasonable to assume that nosocomial CNS bacteremia in neonatal intensive care units might be associated with the use of indwelling vascular lines, as had been suggested by other investigators. We found that CNS cause the majority of nosocomial bacteremias in our neonatal intensive care units and that low birth weight and length of stay are major independent risk factors for these infections. In addition, we confirmed the association of central venous lines with CNS bacteremia but were surprised to find that intravenous administration of lipid emulsion was an even greater risk factor. These observations have brought our work back to the laboratory, where a rabbit model of CNS catheter infection is being studied to explore the relationship between lipid emulsion and catheter colonization and bacteremia.