Respiratory tract infections;

Is it just my imagination or are Covid-19 cases going down as influenza cases are surging out of control during this flu season?

FA Manian MD, MPH, , , , , , , , Leave a comment

No, you are not imagining! Although during respiratory tract infection (RTI) season several viruses such as rhinovirus, respiratory syncytial virus (RSV) and coronavirus may cocirculate, influenza virus frequently outcompetes many RTI viruses, likely through a phenomenon called “viral interference.” 1-4

A negative viral interference is observed when a virus that has already infected a host makes that host resistant to infection by the second virus (isn’t that fascinating?). Although there a lot of virus, host and environmental variables that affect infection risk, potential mechanisms for this interference include a rapid and robust innate immune response to the first virus such as through upregulation of interferon (IFN) production which can protect against unrelated viruses, thereby creating a temporary “antiviral state.” 1-4

A negative viral interference has been shown between influenza-A virus (IAV) and SARS-CoV-2 by a cool 2024 study using the air-liquid interface culture model of the differentiated human airway epithelium. 4 Replicating IAV induced a robust interferon response and suppressed SARS-CoV-2 replication in both sequential and simultaneous infections. In contrast, SARS-CoV-2 did not demonstrate significant viral interference with IAV.  The researchers took their experiment a step further and found that oseltamivir (Tamiflu), an anti-IAV agent, restored SARS-CoV-2 replication with IAV coinfection by reducing induction of IFN!

One explanation for the inability of SARS-CoV-2 to interfere with the production of influenza virus is its slower induction of IFN stimulating genes likely due to its more effective mechanisms of antagonizing the IFN response with infected cells.4 Another explanation is that SARS-CoV-2 has a slower growth rate than IAV, making it more susceptible to being “outgunned” by faster growing viruses. Some strains of IAV may also cause more damage to the epithelial cells than SARS-CoV-2 thus reducing the number of host cells available for SARs-CoV-2 infection.2 Last, secreted IFNs (eg, IFN λ) can also bind to receptors present at the surface of infected and neighboring state blocking the second virus from infecting the host.1

So, it looks like competition among living forms in this world also applies to the world of viruses!

Bonus Pearl: Did you know that the concept of viral interference was first described in the 1960s following observation that oral administration of live enterovirus vaccines decreased detection of several unrelated respiratory viruses such as influenza virus, RSV and human adenovirus?1

Liked this post? Download the app on your smart phone and sign up below to catch future pearls right into your inbox, all for free!

Subscribe to Blog via Email

Enter your email address to subscribe to this blog and receive notifications of new posts by email.

References

  1. Piret J, Bolvin G. Viral interference between respiratory viruses. Emerg Infect Dis 2022;28:273-280. Viral Interference between Respiratory Viruses – PubMed
  2. Gilbert-Girard S, Piret J, Carbonneau J, et al. Viral interference between severe acute respiratory syndrome coronavirus 2 and influenza A viruses. PLOS Pathogens 2024;20(7):e1012017. Viral interference between severe acute respiratory syndrome coronavirus 2 and influenza A viruses – PubMed
  3. Kaaijk P, Swaans N, Nicolaie AM, et al. Contribution of influenza viruses, other respiratory viruses and viral co-infections to influenza-like illness in older adults. Viruses 2022;14, 797. Contribution of Influenza Viruses, Other Respiratory Viruses and Viral Co-Infections to Influenza-like Illness in Older Adults – PubMed
  4. Cheemarla NR, Watkins TA, Mihaylova VT, et al. Viral interference during influenza A-SARS-CoV-2 coinfection of the human airway epithelium and reversal by oseltamivir. J Infect Dis 2024;229:1430-4. Viral Interference During Influenza A-SARS-CoV-2 Coinfection of the Human Airway Epithelium and Reversal by Oseltamivir – PubMed

Disclosures/Disclaimers: The listed questions and answers are solely the responsibility of the author and do not necessarily represent the official views of Mercy Hospital-St. Louis, Massachusetts General Hospital, Harvard Catalyst, Harvard University, their affiliate academic healthcare centers, or its contributors. Although every effort has been made to provide accurate information, the author is far from being perfect. The reader is urged to verify the content of the material with other sources as deemed appropriate and exercise clinical judgment in the interpretation and application of the information provided herein. No responsibility for an adverse outcome or guarantees for a favorable clinical result is assumed by the author. Thank you!

 

 

Is it just my imagination or are Covid-19 cases going down as influenza cases are surging out of control during this flu season?

Should I routinely select antibiotics with activity against anaerobes in my patients with presumed aspiration pneumonia?

FA Manian MD, MPH, , , , , , , , , , , , , , , , , , , , , , , , , , Leave a comment

Anaerobes have been considered a major cause of aspiration pneumonia (AP) based on studies published in 1970’s (1-3). More recent data, however, suggest that anaerobes no longer play an important role in most cases of AP (4-7) and routine inclusion of specific anti-anaerobic drugs in their treatment is no longer necessary.

 
An important reason for anaerobes not playing an important role in AP in the current era is the change in the demographics of patients who may be affected. Patients reported in older studies often suffered from alcohol use disorder, drug ingestion, seizure disorders and acute cerebrovascular accident. In contrast, more recent data show that AP often occurs in nursing home residents, the elderly with cognitive impairment, and those with dysphagia, gastrointestinal dysmotility or tube feeding (8,9).

 
In addition, many cases of AP reported in older studies involved delay of 4 or more days before seeking medical attention and, not surprisingly, often presented with lung abscess, necrotizing pneumonia, empyema, or putrid sputum, features that are relatively rare in the current era.

 
Further supporting the diminishing role of anaerobes in AP, are recent microbiological studies of the respiratory tract in AP revealing the infrequent isolation of anaerobes and, even when isolated, often coexisting with aerobic bacteria. The latter observation is important because, due to the alteration in the redox potential (9,10), treatment of aerobic bacteria alone may lead to less oxygenation consumption and less favorable environment for survival of anaerobes in the respiratory tract.

 
We should also always consider the potential adverse effects of unnecessary antibiotics with anaerobic activity in our frequently debilitated patients, including gastrointestinal dysbiosis (associated with Clostridiodes difficile infections and overgrowth of antibiotic-resistant pathogens such as vancomycin-resistant enterococci (VRE), hypersensitivity reactions, drug interactions, and central nervous system toxicity (11,12).
Thus, the weight of the evidence does not justify routine anaerobic coverage of AP in today’s patients.

Liked this post? Download the app on your smart phone and sign up below to catch future pearls right into your inbox, all for free!

Subscribe to Blog via Email

Enter your email address to subscribe to this blog and receive notifications of new posts by email.

References
1. Bartlett JG, Gorbach SL, Finegold SM. The bacteriology of aspiration pneumonia. Am J Med. 1974;56(2):202-7. https://www.ncbi.nlm.nih.gov/pubmed/4812076
2. Bartlett JG, Finegold SM. Anaerobic pleuropulmonary infections. Medicine (Baltimore). 1972;51(6):413-50. https://www.ncbi.nlm.nih.gov/pubmed/4564416
3. Bartlett JG, Gorbach SL. The triple threat of aspiration pneumonia. Chest. 1975;68(4):560-6. https://www.ncbi.nlm.nih.gov/pubmed/1175415
4. Finegold SM. Aspiration pneumonia. Rev Infect Dis. 1991;13 Suppl 9:S737-42. https://www.ncbi.nlm.nih.gov/pubmed/1925318
5. Bartlett JG. How important are anaerobic bacteria in aspiration pneumonia: when should they be treated and what is optimal therapy. Infect Dis Clin North Am. 2013;27(1):149-55. https://www.ncbi.nlm.nih.gov/pubmed/23398871
6. El-Solh AA, Pietrantoni C, Bhat A, Aquilina AT, Okada M, Grover V, et al. Microbiology of severe aspiration pneumonia in institutionalized elderly. Am J Respir Crit Care Med. 2003;167(12):1650-4. https://www.ncbi.nlm.nih.gov/pubmed/12689848
7. Marik PE, Careau P. The role of anaerobes in patients with ventilator-associated pneumonia and aspiration pneumonia: a prospective study. Chest. 1999;115(1):178-83. https://www.ncbi.nlm.nih.gov/pubmed/9925081
8. Bowerman TJ, Zhang J, Waite LM. Antibacterial treatment of aspiration pneumonia in older people: a systematic review. Clin Interv Aging. 2018;13:2201-13. https://www.ncbi.nlm.nih.gov/pubmed/30464429
9. Mandell LA, Niederman MS. Aspiration Pneumonia. N Engl J Med. 2019 Feb 14;380(7):651-663. doi: 10.1056/NEJMra1714562. https://www.ncbi.nlm.nih.gov/pubmed/30763196
10. Walden, W. C., & Hentges, D. J. (1975). Differential effects of oxygen and oxidation-reduction potential on the multiplication of three species of anaerobic intestinal bacteria. Applied microbiology, 30(5), 781–785. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC187272/
11. Sullivan A, Edlund C, Nord CE. Effect of antimicrobial agents on the ecological balance of human microflora. Lancet Infect Dis. 2001;1(2):101-14. https://www.ncbi.nlm.nih.gov/pubmed/11871461
12. Bhalla A, Pultz NJ, Ray AJ, Hoyen CK, Eckstein EC, Donskey CJ. Antianaerobic antibiotic therapy promotes overgrowth of antibiotic-resistant, gram-negative bacilli and vancomycin-resistant enterococci in the stool of colonized patients. Infect Control Hosp Epidemiol. 2003;24(9):644-9. https://www.ncbi.nlm.nih.gov/pubmed/14510245

 

Contributed by Amar Vedamurthy, MD, MPH, Mass General Hospital, Boston, MA

Should I routinely select antibiotics with activity against anaerobes in my patients with presumed aspiration pneumonia?