Clinical presentation
Sore throat, fevers, chills, myalgias
If severe, will result in hypoxemia and tachypnea.
When to hospitalize
Significant dehydration
If the patient appears septic: respiratory distress, hypoxemia, impaired cardiopulmonary function, AMS.
Imaging
US/CXR show patchy bilateral infiltrates.
CT may show bronchial wall thickening, tree-in-bud nodules, multifocal consolidations.
Testing
Flu PCR has ~ 90% sensitivity, though is dependent on quality of sample (did the swab go deep enough)
Tracheal aspirate or BAL if intubated (gold standard)
Procalcitonin. Influenza generally doesn’t increase procalcitonin à be more suspicious of a bacterial cause.
General sepsis/pneumonia labs: blood and sputum cultures, MRSA PCR, urine
When to suspect a bacterial superinfection
Imaging with lobar consolidations, cavitations, or significant pleural effusion suggests superimposed bacterial PNA, or other diagnosis.
A biphasic illness: when the patient initially improves, then deteriorates again.
Copious sputum production (generally not a feature of influenza)
Is there a role for antivirals?
The evidence is iffy. Cochrane review 2014 of 44 trials, 24,000 patients showed only modest benefits1
Reduction of symptoms by ~ 0.5 days average.
Does not reduce hospitalization or development of pneumonia.
1st line: Tamiflu (oseltamivir) 75mg BID x5 days (10 days if critically ill). PO only.
Most effective within the first 48 hours if the patient is critically ill, give it regardless of illness duration.
2nd line: Peramivir in pt who cannot tolerate oral therapy.
Is there a role for antibiotics?
No… but also yes. There is bacterial superinfection in 1/3rd of patients, and it is generally difficult to exclude bacterial pneumonia until cultures return.
Antibiotic choices include beta-lactam + macrolide + MRSA coverage.
Beta-lactam:
Generally, ceftriaxone.
Broaden to pseudomonal coverage for your HCAP/VAP/immune compromised patients, same as your other pneumonias.
Macrolide
Instead of azithromycin, consider clarithromycin, which has direct antiviral activity against influenza2.
MRSA coverage
High prevalence of MRSA superinfection among influenza pneumonia 3
Linezolid is superior to vancomycin for MRSA pneumonia, unless there is a contraindication4.
A key difference in resuscitation versus traditional sepsis
Most mortality in influenza pneumonia is secondary to ARDS5. Avoid large volume resuscitation. I.e. do not follow the Surviving Sepsis 30cc/kg recommendation.
For mild hypotension, consider low dose pressors instead of large volume fluid resuscitation.
If the patient is normotensive, great. You don’t need to resuscitate blood pressure.
References
1. Jefferson T, Jones MA, Doshi P, et al. Neuraminidase inhibitors for preventing and treating influenza in adults and children. Cochrane Database Syst Rev. 2014;(4). doi:10.1002/14651858.CD008965.pub4
2. Yamaya M, Hatachi Y, Kubo H, Nishimura H. Clarithromycin inhibits pandemic A/H1N1/2009 influenza virus infection in human airway epithelial cells. Eur Respir J. 2012;40(Suppl 56). Accessed December 11, 2023. https://erj.ersjournals.com/content/40/Suppl_56/P4364
3. Uyeki TM, Bernstein HH, Bradley JS, et al. Clinical Practice Guidelines by the Infectious Diseases Society of America: 2018 Update on Diagnosis, Treatment, Chemoprophylaxis, and Institutional Outbreak Management of Seasonal Influenzaa. Clin Infect Dis Off Publ Infect Dis Soc Am. 2019;68(6):e1-e47. doi:10.1093/cid/ciy866
4. Wunderink RG, Niederman MS, Kollef MH, et al. Linezolid in methicillin-resistant Staphylococcus aureus nosocomial pneumonia: a randomized, controlled study. Clin Infect Dis Off Publ Infect Dis Soc Am. 2012;54(5):621-629. doi:10.1093/cid/cir895
5. Severe influenza. EMCrit Project. Accessed December 11, 2023. https://emcrit.org/ibcc/influenza/