Case Study

Lower Respiratory Tract Infection (LRTI):
Is it Viral or Bacterial?

Shawn Depcinski, PharmD, Antibiotic Stewardship

Age, sex:

65-year-old female

Chief complaint:

Cough, wheezing, increasing shortness of breath

Significant medical history:

Advanced chronic obstructive pulmonary disease (COPD), diabetes mellitus (DM)

Admission labs, diagnostics:

Temperature: 38.9°C, white blood cell count (WBC): 14.0 x103/µL, chest x-ray right upper lob infiltrate

Admitting diagnosis:

Acute exacerbation of COPD secondary to community acquired pneumonia (CAP)

Treatment, interventions:

4L nasal cannula, steroids, bronchodilators, ceftriaxone, azithromycin

Follow-up labs:

Procalcitonin (PCT) = 0.12 μg/L, polymerase chain reaction (PCR) nasopharyngeal swab: influenza A positive

Treatment, interventions update:

Oseltamavir started, antibiotics continued due to concern for bacterial co-infection

Day 2:

PCT 0.09 μg/L, temperature decreased to 38.2°C, and oxygen requirements decreased to 2L nasal canula<

Treatment, interventions:

Antibiotic stewardship team recommended to stop antibiotics secondary to low PCT levels, which was accepted by the medical team


Over the next four days, patient continued to improve and was discharged to home

Key takeaways

Bacterial co-infection may occur in approximately one-fourth of hospitalized patients with influenza.1 PCT has a high negative predictive value (NPV) at ≤ 0.25 μg/L, which aids in determining the need for antibiotics in LRTI. When uncertainty exists with an initial negative PCT result, repeating the test within 6 to 24 hours can assist with confirming the initial result, and indicate that antibiotics may no longer be necessary. In this case, PCT aided in ruling out bacterial infection, allowing the clinicians to avoid giving unnecessary antibiotics and to continue with the appropriate anti-viral therapy.


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  1. Klein EY, Monteforte B, Gupta A, Jiang W, May L, Hsieh YH, et al. The frequency of influenza and bacterial coinfection: a systematic review and meta-analysis. Influenza Other Respir Viruses. 2016 Sep;10(5):394-403.