Approach to a fever (0-60 days): Clinical sciences

Fever in infants 60 days of age and younger is defined as a body temperature of 38 degrees Celsius, or 100.4 degrees Fahrenheit, or higher. Infants in this age group have a higher risk of invasive bacterial infection, when compared with older infants, so it’s important to promptly identify and treat the source of a fever. Young infants can be stratified by age and initial lab findings in order to guide the subsequent diagnostic workup and determine the need for treatment.

If a patient 60 days of age or younger presents with a fever, you should first perform an ABCDE assessment. If the patient is unstable, stabilize the airway, breathing, and circulation. Next, obtain IV access, and consider starting IV fluids. Begin continuous vital sign monitoring, including blood pressure, heart rate, and oxygen saturation, and provide supplemental oxygen if needed.

Okay, now let’s go back to the ABCDE assessment and look at stable patients. First, obtain a focused history and physical exam, and make sure to ask about exposure to sick individuals. Febrile infants often have vague symptoms, like fussiness, lethargy, and poor oral intake. Occasionally, caregivers might report symptoms that suggest a focus of infection, such as diarrhea, vomiting, cough, nasal congestion, or rash. Be sure to ask about perinatal and birth history.

The physical exam will confirm a temperature of 38 degrees Celsius or higher, frequently with an elevated heart rate. Next, you might notice signs of respiratory distress, like nasal flaring, grunting, or retractions, as well as abnormal lung sounds, like crackles and wheezing. Finally, the abdomen exam might reveal distention or tenderness. The presence of a fever, with or without other findings, in an infant 60 days or younger, should make you suspect infection.

To search for a focus of infection, order basic labs, including a CBC, inflammatory markers such as CRP and procalcitonin, and a blood culture. In addition, send urine obtained by suprapubic aspiration or catheterization for urinalysis, and reserve a sample of urine to send for culture if needed.

Now that you’ve ordered initial labs, your next step is to assess your patient’s age in order to determine how to proceed with the diagnostic workup.

First, let’s discuss febrile infants under 8 days of age. For these patients, you’ll need to perform a full evaluation for sepsis, including urine and CSF cultures. Next, hospitalize your patient, and start empiric parenteral antibiotics such as ampicillin in combination with gentamicin or cefotaxime. Additional diagnostic evaluation requires careful consideration of the perinatal history and other individual factors.

Here’s a clinical pearl to remember! Don’t delay initiation of antibiotics to get a lumbar puncture for CSF cultures.

Now, let’s focus on the evaluation of infants between 8 and 21 days of age. First, you'll need to send urine for culture, perform a lumbar puncture, and send CSF for analysis, which includes gram stain and culture, cell count, and protein and glucose levels. Don’t forget to consider HSV infection, so assess your patient's risk factors, which include maternal fever or genital lesions during the perinatal period.

Additionally, be on the lookout for signs of HSV infection, such as mucous membrane ulcers, skin vesicles, seizures, or hypothermia. If you identify any of these risk factors, order HSV testing as well. Next, admit your patient to the hospital, and start empiric parenteral antibiotics such as ampicillin in combination with gentamicin or cefotaxime, as well as IV acyclovir if you are suspecting an HSV infection.

Finally, let’s turn our attention to infants between the ages of 22 and 60 days. For this age group, you’ll need to assess the inflammatory markers and urinalysis to guide additional decision-making. Urinalysis is abnormal if the leukocyte esterase is positive, or if there are more than 5 WBCs per high power field in a centrifuged sample.

Let’s first consider what to do if either the CRP or procalcitonin is abnormal, regardless of urinalysis results. In this case, you should order urine cultures only if the urinalysis is abnormal, otherwise, you should primarily focus on CSF analysis. More specifically, if your patient is 22 to 28 days old and has abnormal inflammatory markers, you should always perform a lumbar puncture and order a CSF analysis and culture. On the other hand, if your patient is 29 to 60 days old and has abnormal inflammatory markers, you should consider ordering CSF analysis and culture after weighing the risks and benefits. Next, admit your patient to the hospital and begin empiric parenteral antibiotics, while you are waiting for culture results.

On the other hand, if the CRP and procalcitonin are normal, but the urinalysis is abnormal, you should first order a urine culture. Next, apply clinical judgment and shared decision-making with the patient’s caregiver, to determine whether to obtain CSF analysis and culture. Regardless of whether you decide to perform a lumbar puncture, administer parenteral antibiotics to all febrile infants 22 to 28 days of age, and admit them to the hospital, pending culture results. For febrile infants 29 to 60 days of age with normal inflammatory markers and abnormal urinalysis, use shared decision-making to decide whether to hospitalize your patient and treat with empiric parenteral antibiotics; or discharge your patient home with oral antibiotics and follow-up within 24 hours.