Podcast #174 - EB Medicine: The Febrile Young Infant

It is time for another EB Medicine special.  The febrile young infant can be one of the scarier patients for a variety of reasons.  They are so young they are unable to communicate, they have very real and serious pathogens that can have deadly consequences, and the family as well as other individuals taking care of the patient can be nervous or scared creating increased stress.  In this post, we cover EB Medicine's recent article on this topic to better improve your practice.

For access to this article make sure to click this link.  If you do not have a subscription yet with EB Medicine you will not be able to get the associated CME.  However, check out the end of our show notes to learn how you can get access and at a great discount.

​Sometimes the process to evaluate and treat the febrile young infant can seem very structured and methodical, especially at first glance.  However, with different age ranges and a variety of data over time demonstrates that this is not totally the case.  While the most structured and "routine" approach would be for neonates, there are even special considerations in these populations.  We will break down some of the key highlights from the article to help guide us in our management based on the current evidence.

First, why is this such a big deal?  Due to their immature immune system, there is a high-risk for seriously bacterial infections (SBIs) and invasive bacterial infections (IBIs) in children aged 60-90 days or less.  What makes it more challenging is the lack of social responsiveness (social smile), verbal cues, and that even in the well-appearing young infant they can still harbor serious infections.  Additionally, there is a medico-legal component as the most common diagnosis in pediatric medical malpractice claims from the emergency department is bacterial meningitis.

Key Definitions:

• Neonate: 28 days old or less
• Young Infant: 90 days old or less (some cutoffs are 60 days or less)
• Fever: rectal temperature of 38 degrees Celsius or higher (100.4 F)
• Serious Bacterial Infection (SBI): variety of conditions that in some cases can be invasive (IBI)
  • Bacterial meningitis (IBI)
  • Bacteremia/sepsis (IBI)
  • Urinary tract infection (UTI) or pyelonephritis (most common)
  • Pneumonia (focal consolidations)
  • Bacterial enteritis
  • Cellulitis
  • Abscess
  • Osteomyelitis
  • Septic arthritis
• Full septic workup
  • Complete blood cell (CBC) count +/- C-reactive protein (CRP) and procalcitonin (PCT) if available
  • Blood culture
  • Urinalysis with culture
  • Serum glucose
  • Complete metabolic panel (CMP) to include liver enzymes
  • Cerebrospinal fluid (CSF) cell count, glucose, protein, and culture
  • Stool culture (as indicated)
  • Chest x-ray (as indicated)
  • Herpes simplex virus (HSV) testing (as indicated)

Causes for fever in well-appearing young infants:

• Serious bacterial infection (SBI)
  • UTI
  • Bacteremia
  • Bacterial meningitis
  • Pneumonia
  • Soft tissue cellulitis
  • Bacterial enteritis
  • Bone and joint infections
• Viral infections
  • Enterovirus infection
  • Upper respiratory tract (URI) infection
  • Bronchiolitis
  • Viral gastroenteritis
  • Neonatal HSV infection

Causes for fever in ill-appearing young infants:

• Infectious causes
  • SBIs
  • Neonatal HSV infection
  • Enterovirus infection
  • Respiratory syncytial virus (RSV) infection
• Cardiac causes (usually  not febrile)
  • Ductal-dependent left-sided or right-sided obstructive lesions
• Metabolic causes (also may be ill-appearing without a fever)
  • Inborn errors of metabolism
  • Congenital adrenal hyperplasia
• Gastrointestinal causes (can also be without a fever)
  • Malrotation with volvulus

The diagnosis of HSV can be rather challenging.  Its presentation can vary depending on if it involves skin and mucous membranes, the central nervous system, or it is disseminated.  EB Medicine has a great table to help break down  the complexities.

The history and physical is a vital component to our evaluation in addition to lab findings:

• History
  • Method of temperature measurement (rectal, tympanic, axillary, forehead, etc)
  • Viral symptoms (congestion, runny nose, etc)
  • Feeding (poor or slow)
  • Urine and stool output
  • Fussiness and/or lethargy
  • Birth history including gestational age at birth
  • Prenatal laboratory studies (such as screening for group B strep and HSV)
  • Family history of early, unexplained deaths or metabolic disease
• Physical Exam
  • Difficult to arouse or console  (bouncing infant that is more upset compared to rest may be meningeal irritation seen with meningitis)
  • Anterior fontanel fullness or elevation
  • Jaundice
  • Acute otitis media
  • Respiratory exam including tachypnea, accessory muscle use, crackles, or wheezing
  • Murmur
  • Weak pulses

There are a variety of risk-stratification tools with varying types of data and suggestions.    The most common along with their year of publication are the Boston Criteria (1992), Philadelphia Criteria (1993), Rochester Criteria (1994), Step-by-Step (2016), and PECARN (2019).     The last three have MDCalc breakdowns to remind us of the cutoffs and criteria.  It is also important to know that the last one, PECARN (Pediatric  Emergency Care Applied Research Network) has  not yet been externally validated and should currently be used only in infants aged 29-60 days.  This is due to elevated herpes meningoencephalitis risk and and limited numbers of episodes of bacterial meningitis in neonates.

It is vital to remember no matter what method we use that we involve our pediatrician colleagues in the decision making process.  In the case of those who are not as familiar with  or comfortable in managing the febrile young infant to have additional support.  This can be in the form of that pediatrician or even another one of our emergency medicine colleagues.  Whatever the case, the more support we have the better.

Final Pearls from the Article:

• Young infants with a fever can harbor dangerous pathology and not be ill-appearing
  
  • Given the rates of SBIs and IBIs in infants that only had a tactile fever or a fever at home they should still undergo the same level of testing as those with a documented fever in the department
  • Remember that there can be non-infectious causes for young infants to be ill-appearing or in shock
• Neonates all need a full septic workup and admission
  • They have the highest prevalence of SBI and IBI but the least reliable exam
  • CSF testing of all neonates is necessary
  • Consider testing for HSV in the neonates aged 21 days or less
• There are changes to the recommendations in testing
  • Newer algorithms incorporate CRP and PCT into their tests
    
  • Chest x-ray is unnecessary unless respiratory signs or symptoms are present
  • Stool studies such as culture and fecal leukocytes for bacterial gastroenteritis should also be obtained based on symptoms (ie, blood or mucus in the stool)

• UTIs and the bacterium E. coli is the most common infection and bacterium identified in febrile young infants 
• Rapid antigen testing and/or polymerase chain reaction (PCR) testing for respiratory viruses should be sent for all febrile infants with rhinorrhea, nasal congestion, or bronchiolitis
  • However, in infants 60 days or younger they can still have other infections (usually UTIs)
  • Remember that apnea may be the only finding in bronchiolitis for children less than six weeks of age
• All young infants less than 90 days of age should be tested for UTI
• Young infants without a clear source of infection and no CSF obtained should not receive empiric antibiotics as  this can make the diagnosis of meningitis difficult to do later

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