Utility of investigation for suspected microbial keratitis: a diagnostic accuracy study.

PURPOSE: The true disease status of a population with suspected microbial keratitis (MK) cannot be verified. There is not an accurate (gold) reference standard to confirm infection and inter-test comparisons of sensitivity and specificity therefore lead to bias with questionable estimates of test utility. We present an alternative method to report results. METHODS: We used a decision to treat as the definition for MK. We retrospectively compared the results of corneal culture and polymerase chain reaction (PCR) as these are objective tests available for the three principal groups of pathogens. We then estimated the potential contribution of positive results, either alone or in combination, to support the working diagnosis. RESULTS: We included 2021 (77.4%) eyes with suspected bacterial keratitis, 365 (14.0%) with suspected acanthamoeba keratitis, and 226 (8.6%) with suspected fungal keratitis, all treated between July 2013 and December 2019. In these groups, there were 51.6% positive culture and 6.5% positive PCR results for bacteria, 19.0% and 40.5% for acanthamoeba, and 28.3% and 15.0% for fungi. Between groups the differences in the proportions of positive results from culture and PCR was statistically significant (P < 0.001). The added benefit of PCR to the result of culture in identifying a potential pathogen was 1.4% for bacteria (P = 0.6292), 24.4% for acanthamoeba (P = 0.0001), and 5.8% for fungi (P = 0.3853). CONCLUSIONS: For suspected MK a comparison of the test positivity rate is an easily comprehensible outcome measure of test utility.

What you need to know about microbiology referrals.

Microbiologists are frequently consulted for guidance on the investigation and management of infection, including antimicrobial prescribing in hospital settings. There is a rising demand for timely microbiology advice in the context of increasing global travel and antibiotic resistance, which give rise to complex cases. However, junior doctors are seldom trained in making effective referrals. Improving confidence in this key skill saves time for both the referring clinician and the specialist, and results in more accurate advice being given. This benefits patients who are more likely to receive appropriate treatment. This article presents guidance, developed in consultation with specialists, to improve the quality of referrals to microbiologists. This includes the information required for a high-quality referral, and signposts referring clinicians to existing resources which are suitable for simpler cases not requiring specialist input.

Comparison of culture, confocal microscopy and PCR in routine hospital use for microbial keratitis diagnosis.

AIMS: To evaluate the sensitivity and specificity of polymerase chain reaction (PCR), in vivo confocal microscopy (IVCM) and culture for microbial keratitis (MK) diagnosis. METHODS: Retrospective review of PCR, IVCM and culture results for MK diagnosis at Moorfields Eye Hospital between August 2013 and December 2014. RESULTS: PCR results were available for 259 MK patients with concurrent culture for 203/259 and IVCM for 149/259. Sensitivities and specificities with 95% confidence intervals [95% CI] were calculated for Acanthamoeba keratitis (AK) and fungal keratitis (FK), by comparison with culture, for both IVCM and PCR. For AK, FK and bacterial keratitis (BK) sensitivities were calculated, for each diagnostic method, by comparison with a composite reference standard (a positive result for one or more of culture, PCR or IVCM having a specificity of 100% by definition). For the latter, sensitivities with [95% CI] were: for AK, IVCM 77.1% [62.7-88.0%], PCR 63.3% [48.3-76.6%], culture 35.6 [21.9-51.2]; for FK, IVCM 81.8% [48.2-97.7%], PCR 30.8% [9.09-61.4%], culture 41.7% [15.2-72.3%]; for BK, PCR 25.0% [14.7-37.9%], culture 95.6% [87.6-99.1%]. CONCLUSION: IVCM was the most sensitive technique for AK and FK diagnosis but culture remains our gold standard for BK. These findings reflect results to be expected from service providers to UK ophthalmology units and demonstrates the need at our centre for ongoing diagnostic result audit leading to the potential to improve PCR diagnosis. Both FK and AK are now common in the UK; ophthalmology units need to have all these techniques available to optimise their MK management.

Bacterial keratitis: identifying the areas of clinical uncertainty.

Bacterial keratitis is a common corneal infection that is treated with topical antimicrobials. By the time of presentation there may already be severe visual loss from corneal ulceration and opacity, which may persist despite treatment. There are significant differences in the associated risk factors and the bacterial isolates between high income and low- or middle-income countries, so that general management guidelines may not be appropriate. Although the diagnosis of bacterial keratitis may seem intuitive there are multiple uncertainties about the criteria that are used, which impacts the interpretation of investigations and recruitment to clinical studies. Importantly, the concept that bacterial keratitis can only be confirmed by culture ignores the approximately 50% of cases clinically consistent with bacterial keratitis in which investigations are negative. The aetiology of these culture-negative cases is unknown. Currently, the estimation of bacterial susceptibility to antimicrobials is based on data from systemic administration and achievable serum or tissue concentrations, rather than relevant corneal concentrations and biological activity in the cornea. The provision to the clinician of minimum inhibitory concentrations of the antimicrobials for the isolated bacteria would be an important step forward. An increase in the prevalence of antimicrobial resistance is a concern, but the effect this has on disease outcomes is yet unclear. Virulence factors are not routinely assessed although they may affect the pathogenicity of bacteria within species and affect outcomes. New technologies have been developed to detect and kill bacteria, and their application to bacterial keratitis is discussed. In this review we present the multiple areas of clinical uncertainty that hamper research and the clinical management of bacterial keratitis, and we address some of the assumptions and dogma that have become established in the literature.

Evaluation of a Novel Culture System for Rapid Pathogen Identification and Detection of Cephalosporin Resistance in Neonatal Gram-negative Sepsis at a Tertiary Referral Unit in Harare, Zimbabwe.

BACKGROUND: Neonatal sepsis accounts for a large proportion of neonatal deaths in sub-Saharan Africa. The lack of access to diagnostic testing and excessively long turnaround times to result contributes to delays in sepsis identification and initiation of appropriate treatment. This study aims to evaluate the novel InTrays COLOREX Screen and extended-spectrum beta-lactamase for rapid identification of bacterial pathogens causing sepsis and detection of resistance. METHODS: Neonates with suspected sepsis admitted to the Harare Central Hospital were prospectively enrolled. One blood culture was collected and incubated using the BacT/ALERT automated system. Positive blood cultures with potential pathogens identified by Gram stain were inoculated on the InTray COLOREX Screen and extended-spectrum beta-lactamase culture plates. RESULTS: A total of 216 neonates with suspected sepsis were recruited. Pathogens were isolated from blood cultures in 56 (25.9%) neonates of which 54 were Klebsiella pneumoniae. All K. pneumoniae were resistant to ceftriaxone and 53 (98%) were resistant to gentamicin. Sensitivity and specificity for ceftriaxone-resistant K. pneumoniae detection using InTrays were 100%. InTrays results were interpretable as early as 5-10 hours (median 7 hours, interquartile range 7-7) post blood culture positivity enabling rapid identification and notification of result and leading to a 60% reduction in time to result from blood culture collection. CONCLUSIONS: This study shows that the implementation of a novel culture method was feasible and reduced turnaround times for results by 60% compared with standard microbiologic techniques. An impact on patient outcomes and cost-effectiveness of this method needs to be demonstrated.

Clinical outcomes of teicoplanin use in the OPAT setting.

Teicoplanin possesses several convenient properties for use in the delivery of outpatient parenteral antimicrobial therapy (OPAT) services. However, its use is not widespread and data on its efficacy in the OPAT setting are limited. Here we present a case series of patients undergoing OPAT care being treated by either teicoplanin-based (n = 107) or ceftriaxone-based (n = 191) antibiotic regimens. Clinical failure with teicoplanin occurred in five episodes of care (4.7%) compared with only two episodes of ceftriaxone-based OPAT care (1.0%). Teicoplanin-associated clinical failure was observed in 2 (33.3%) of 6 patients with Enterococcus infections compared with 3 (3.0%) of 101 patients with non-Enterococcus infections. Overall, there were four (2.9%) drug-related adverse events for teicoplanin and four (1.8%) for ceftriaxone, prompting a switch to teicoplanin in three patients. These findings support the continued use of teicoplanin in OPAT as well as its consideration in centres where it is not currently being offered.

How to use Procalcitonin.

Diagnosing bacterial infection in the unwell or febrile child is a common challenge faced by all paediatricians. Despite the advent of novel molecular techniques, there is ongoing need for diagnostic assays with adequate performance and turnaround time to facilitate safe clinical decision-making when bacterial sepsis is suspected, such as whether to commence empirical treatment with antibiotics. Procalcitonin is an established marker of infection that has a potential role in the diagnosis and exclusion of serious or invasive bacterial infection in neonates and children. Although enthusiastically adopted in many countries and institutions, national guidance in the UK does not yet support its routine use. This article reviews the relevant literature on the use of procalcitonin measurement in common paediatric clinical scenarios.

Viral haemorrhagic fever in children.

Viral haemorrhagic fevers (VHFs) are currently at the forefront of the world's attention due to the recent Zaire ebola virus epidemic in West Africa. This epidemic has highlighted the frailty of the world's public health response mechanisms and demonstrated the potential risks to nations around the world of imported cases of epidemic diseases. While imported cases in children are less likely, the potential for such a scenario remains. It is therefore essential that paediatricians are aware of and prepared for potential imported cases of tropical diseases, VHFs being of particular importance due to their propensity to cause nosocomial spread. Examining the four families of viruses--Filoviridae, Arenaviridae, Bunyaviridae and Flaviviridae--we describe the different types of VHFs, with emphasis on differentiation from other diseases through detailed history-taking, their presentation and management from a paediatric perspective.

Herpes simplex virus and varicella zoster virus: recent advances in therapy.

PURPOSE OF REVIEW: The mainstay of antiviral therapy for the alpha-herpesviruses [herpes simplex virus (HSV)-1, HSV-2, and varicella zoster virus (VZV)] over the past 40 years has been the nucleoside analogues such as aciclovir. Although conventional antiviral therapy has reduced mortality in severe disease, novel agents are needed to address the emergence of resistance and toxicity associated with current second-line therapy. Treatment and prophylaxis of VZV and HSV reactivations remains a challenge. RECENT FINDINGS: A number of compounds have recently been evaluated in human clinical trials, amongst them brincidofovir, an intracellularly acting derivative of cidofovir currently undergoing phase III trials. The helicase-primase inhibitors are a new class of antiviral agent and may circumvent resistance to existing agents. Amenamevir and pritelivir are two examples of these agents that have been evaluated clinically along with novel nucleoside analogues such as valomaciclovir and FV-100. Tenofovir, an agent used in HIV and hepatitis B therapy, may also have a role in the prevention of HSV-2 acquisition and reduce viral shedding. SUMMARY: Although several novel antiviral agents have undergone clinical trials in recent years, all are yet to gain licensure. Brincidofovir appears to be the candidate with most promise for adoption into routine practice in the near future.

How to use... blood cultures.

Positive blood culture is the gold standard for diagnosing bacteraemia and fungaemia, yet there is significant variability in aspects of performing and interpreting the test in children and neonates. Processing a blood culture can take several days, and includes use of semi-automated incubation with growth detection and a broad range of laboratory techniques such as Gram staining, phenotypic or molecular identification and antimicrobial susceptibility testing on a cultured isolate. Sensitivity and specificity of a blood culture and time-to-positivity depend on a number of factors related to host/pathogen interaction, collection and transport of the specimen to the laboratory and methods employed to process the specimen. Interpretation of a positive result relies on correlation of the identity of the cultured microorganism with the clinical assessment of the child.