Category: Infectious Disease

Skipping the LP in Infants 30-90 Days – Eh.

This is another one of those “practice-changing” types of articles, where the authors try to debunk some specific aggressive diagnostic or therapeutic modality that is over-utilized in a low-prevalence, high-risk population.  This article, which you may have already seen, is regarding the need for a lumbar puncture in infants between 30 and 90 days.

They perform a retrospective review of nonconsecutive infants between 30 and 90 days of age who presented to the Emergency Department and received the “septic workup” – urinalysis/culture, blood culture, and lumbar puncture/CSF culture.  They analyze a data set of 392 infants, the overwhelming majority of which are completely culture negative.  52 of them are culture positive on their urinalysis, 13 are culture positive in the blood, and 4 are CSF culture positive.  The authors note that only one patient who had a positive urinalysis also had a positive CSF fluid culture – and that infant did not qualify as a low-risk infant by the Rochester criteria – so a well-appearing infant with a positive urinalysis need not undergo LP.

So, essentially, this study tells us only that meningitis is rare and that UTIs are common.  The authors attempt to make the flawed logical argument against LP in their discussion by emphasizing the negative predictive value for meningitis in the setting of an abnormal UA is 98.2%.  However, they erroneously discount the negative likelihood ratio of 0.87 (95% CI, 0.5–1.5).  Therefore, statistically speaking, based on their results, repeating this study 100 times could lead to nearly half the study results showing a positive urinalysis favored concomitant meningitis.

Now, in a clinical sense, the authors are likely correct.  An infant who looks well, meets the Rochester criteria, has an identified source for fever, and will be receiving antibiotics is at low risk for meningitis – by prevalence alone, not by anything this study shows – and is probable to have a good clinical outcome since they’re receiving antibiotics (in the event that same organism is resulting in a well-appearing, subclinical systemic and cerebrospinal bacteremia).  The argument should not be that you can generate a zero-risk population with their combination of +UA and Rochester, but that the risk of bad outcome may be similar to the risk of harms associated with the lumbar puncture, false positives, and follow-on treatment/testing.

“Is a Lumbar Puncture Necessary When Evaluating Febrile Infants (30 to 90 Days of Age) With an Abnormal Urinalysis?”

Computers – Probably Better Doctors for UTI

Uncomplicated urinary tract infections are probably one of the diagnoses that Emergency Physicians handle the worst – if they come to the ER, they’re likely to get some sort drawn-out testing, whereas, if they went to their regular physician or called the nurse hotline, there would be antibiotics waiting for them at the pharmacy before they finished talking.

This is a prospective study in which patients with possible UTI were referred to a triage kiosk to complete a standardized computer questionnaire.  624 patients with possible UTI interacted with the kiosk – and unfortunately, only 103 qualified for the study by having enough features of typical, low-risk illness.  Patients were then randomized to protocolized antibiotic prescription as reviewed by a triage physician or usual care.

The good news – the kiosk saved a lot of time (89 minutes vs. 146 minutes).  The bad news – there were only 41 patients  followed-up in the intervention group and 26 followed-up in the control group, so we end up with only a tiny number of patients in each arm.  The kiosk group received more antibiotics for negative urine cultures than the control group (93% vs. 67%), so there is some additional element of harm secondary to antibiotic exposure – and, with a limited protocol, there are potential misses – and this study isn’t large enough to identify them.

But, really, uncomplicated, typical UTI symptoms in women shouldn’t be rocket science – and you shouldn’t necessarily be doing any testing.  I would say the computer is a better physician – except, it would be absolutely simple for a physician to simply narrow their approach to match the efficiency of the kiosk with, in theory, some added skill.

“A Randomized Trial of Computer Kiosk–expedited Management of Cystitis in the Emergency Department”

ECMO For Influenza

Not many institutions in the U.S. are set up for ECMO in adults, particularly in the Emergency Department, but there are several small datasets out there indicating it should be a significant part of our arsenal for selected patients.  This is a review of ECMO’s use in H1N1 influenza-associated ARDS in England during the “Swine Flu” pandemic.

The authors retrospectively reviewed 80 patients with H1N1 from prospectively collected cohort data, all of whom required critical care for ARDS and were referred for ECMO in the United Kingdom.  Through some data calisthenics, these 80 patients were compared to matching subgroups of patients out of 1,756 in the H1N1 critical care cohort.  Of the 80 patients referred for ECMO, only 69 actually received it.  However, when compared to these 80 patients in an intention-to-treat analysis, there was a significant survival advantage associated with referral to ECMO – approximately 24% mortality in the ECMO-referral group compared to 46-52% in the matched controls, depending on which method they used to identify matched controls.
Not a big stretch to interpret this as a positive treatment association for ECMO in H1N1-associated ARDS.  But, I’d still get your flu shot.
“Referral to an Extracorporeal Membrane Oxygenation Center and Mortality Among Patients With Severe 2009 Influenza A(H1N1)”

Linezolid Is Superior To Vancomycin For Pneumonia

This is consistent with prior studies and not particularly earthshaking, but if you needed more literature to support switching antibiotics in the case of treatment failure, this would be another one.

This is in pigs, and it’s an animal model of MRSA ventilator-associated pneumonia.  Four groups – controls, twice-daily vancomycin, continuous vancomycin infusion, and linezolid.  Treatment was initiated after 12 hours of bacterial inoculation in ventilated pigs.  At the end of their 96 hour treatment period, 75% of controls, 11% of each vancomycin group, and 0% of linezolid pigs were BAL positive for MRSA by culture.  Likewise, pathologic sections also showed decrease inflammation and damage in the linezolid group.

Short story, linezolid is better – but not quite better enough that we can’t still start with vancomycin and keep it in reserve.

Sponsored by Pfizer and Eli Lilly.

“Efficacy of linezolid compared to vancomycin in an experimental model of pneumonia induced by methicillin-resistant Staphylococcus aureus in ventilated pigs”
www.ncbi.nlm.nih.gov/pubmed/21926613

We’re Covered in Filth

This is not the first study showing physician white coats and nursing uniforms are colonized with bacteria, nor that may of those bacteria are pathogenic and multi-drug resistant.  In the past, this has been used as a call for the abolishment of physician white coats, ties, and all long-sleeved apparel.

This study, however, shows that short-sleeved nursing uniforms were just as likely to be coated with bacteria – 49% to 54%.  Interestingly, even “changing uniform daily” still resulted in colonization with pathogenic bacteria.  The authors speculate the main issues are that all textiles easily transmit bacteria, and that hand hygiene might be more critical than uniforms in prevent transmission from patients to physician clothing.

This study also, like the many before it, doesn’t demonstrate anything but colonization – not documented patient-to-patient transmission via healthcare worker clothing or any specific outcome measures.  However, I am a believer that white coats are fomites and medical relics that should go the way of bloodletting and golden elixirs. The studies in support of white coats cite patient satisfaction and ease of identification of roles – which, while important, could be mitigated by new interventions for identification of healthcare providers.  Even though we yet have no evidence of harms from this colonization with pathogenic bacteria, it’s essentially a zero-cost intervention to stop wearing white coats and ties – so even if the number needed to treat to prevent a transmissible infection is immense, it’s a free way to protect our patients as best we can.

“Nursing and Physician Attire as Possible Source of Nosocomial Infections.”
www.ncbi.nlm.nih.gov/pubmed/21864762

New Pediatrics UTI Guidelines

For children between 2 and 24 months of age, the relevant high points for EM:
 – Don’t use bag urines.  Catheterization or suprapubic aspiration is the only acceptable way to make a diagnosis.  However, if you’re stuck, and you have to use a bag, a completely normal bag urine is diagnostic.
 – Send a culture to definitively establish the diagnosis based on pyuria and/or bacteruria and the presence of at least 50,000 CFU/mL of a uropathogen.
 – Oral antibiotic recommendations listed include amoxicillin-clavulanate, trimethoprim-sulfamethoxazole, and a range of oral cephalosporins for at least 7 days.  They do not have any evidence to compare 7, 10, and 14 day courses.  Nitrofurantoin is not appropriate.

Nothing terribly earthshaking – seems all pretty reasonable.

“Urinary Tract Infection: Clinical Practice Guideline for the Diagnosis and Management of the Initial UTI in Febrile Infants and Children 2 to 24 Months.”
pediatrics.aappublications.org/content/early/2011/08/24/peds.2011-1330

Good Thought, But It’s Not Pertussis

A Swiss study in which only 2.5% percent of 1,049 pediatric ambulatory and hospitalized patients presenting with a cough-illness and who were tests for pertussis were culture positive for B. pertussis or parapertussis.  Probably a relatively accurate picture of the general prevalance of pertussis in a non-outbreak situation.  They additionally report that viral superinfection is rare enough to be coincidental – 0.6% – although the authors do note other studies have reported higher incidence, particularly in RSV+ hospitalized children <6 months of age.

So, this data is out the window if there’s an outbreak situation, but the overall clinical take home is that, yet again, our index of suspicion may be too high for an infrequently diagnosed condition – and we should moderate testing in the lower acuity cases.

“Bordetella pertussis and Concomitant Viral Respiratory Tract Infections are Rare in Children With Cough Illness.”
www.ncbi.nlm.nih.gov/pubmed/21407144

Viral or Bacterial Infection? A Blood Test

This is another “someday, in the future” article that made the rounds with the news releases yesterday – where, supposedly, within a few hours of infection, there are significant differences in phagocyte chemiluminescence that allow researchers to differentiate between viral and bacterial infections.

As usual, the breathless commentary is a little ahead of the actual research results.  What the authors did was a data-mining experiment from 69 patients, each of whom had been diagnosed (through standard clinical practice) with either a viral infection, or a bacterial infection.  They ran all the polymorphonuclear leukocytes through their assay, recorded several different sorts of chemoluminescence, and then let computer software do a partitioning analysis to determine the most predictive patterns for bacterial and viral infections.

The software trained to 94.7% accuracy on the “knowns”, and then, when tested on a confusion sample with 18 “unknowns” it was 88.9% accurate.

So, still not good enough for clinical use as a dichotomous result, but if it were allowed to return an equivocal range that quantified the assay uncertainty, then perhaps it could have a role in clinical practice.  In theory, an assay such as this might otherwise reduce additional testing and help reduce the number of viral infections that receive antibiotics.

“Differentiation Between Viral and Bacterial Acute Infectious Using Chemiluminescent Signatures of Circulating Phagocytes”
http://www.ncbi.nlm.nih.gov/pubmed/21517122

It’s Impossible To Catch All Pediatric Pneumonia

Another glass half-full vs half-empty, depending on how you read it.  Their editor capsule summary says “Children without hypoxia, fever, and ausculatory findings are low risk.”  The numbers say – in the absence of hypoxia, fever, or focal ausculatory findings, radiographic pneumonia was seen in 7.6% (CI 5.3-10.0).  Interesting numbers that, to me, say that pediatric pneumonia is still a black box of uncertainty.

However, what the authors call “definite” pneumonia was only 2.9% in the absence of those findings, and the editor’s capsule conclusion is that low-risk patients are best served by follow-up rather than radiology.  And, this is where the half-full/half-empty comes in – because a lot of EPs don’t want to the guy that sends home pneumonia even in a “low risk” situation, given than 30% of their pneumonia diagnoses required admission.  I’d rather take the half-full approach – recognizing that the majority of radiographic pneumonias are viral anyway, and, if the patient has adequate follow-up and tunes up nicely, do my best to avoid unnecessary testing in a low pretest probability setting that will end up with more false positives and unnecessary antibiotics.

“Prediction of Pneumonia in a Pediatric Emergency Department”

It’s Not An Abscess (Yes It Is)

These studies pretty much all end up saying the same thing – academic faculty can’t agree on the presence or absence of differentiating characteristics between abscess and cellulitis.  This particular study is in a pediatric population, and, there’s a lot of kappa and absolute agreement to comb through in their tables, but, basically, about 20% of the time two attendings substantially disagreed.  The authors then follow this up by observing that an I&D was performed 75% time, and purulent material was found 92% of the time.

The best conclusion from this might be – if there’s some ambiguity, put a scalpel in it.  I’d say this is reasonable – because we’ve seen a hundred times the child who bounces into the ED on day 3 of cephalexin for cellulitis because what he really had was a MRSA abscess to begin with.

Or, if you have an ultrasound with a high-frequency probe, you might be able to differentiate homogenous hyperemia from fluid collection.

“Interexaminer Agreement in Physical Examination for Children With Suspected Soft Tissue Abscesses”
www.ncbi.nlm.nih.gov/pubmed/21629150