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Year : 2019  |  Volume : 6  |  Issue : 2  |  Page : 9-12

Pathogen analysis of bacterial pneumonia secondary to influenza

Department of Respiratory and Critical Care Medicine, Peking University Third Hospital, Beijing, China

Date of Web Publication16-Jun-2020

Correspondence Address:
Bei He
Department of Respiratory and Critical Care Medicine, Peking University Third Hospital, Beijing
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/cai.cai_4_20

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In human history, there have been several times of influenza raging, which have caused tens of millions of deaths and brought serious social and economic burdens. Although with the development of science, the emergence of vaccines has significantly reduced the incidence and mortality of influenza, due to the high variability of viruses, there is still a lack of effective treatment. More and more studies have found that bacterial pneumonia secondary to influenza was an important cause of the progression to critical illness or even death. Hence, diagnosis and treatment timely of secondary bacterial pneumonia are valuable. Therefore, we discuss the pathogens of bacterial pneumonia secondary to influenza, associated morbidity, mortality, and risk factors. Hopefully, it can provide some valuable references for clinical practice. Since some clinical studies have not separated pneumonia from lower respiratory tract infections, we will discuss these two situations together.

Keywords: Bacterial pneumonia, influenza, pathogen

How to cite this article:
Wang F, He B. Pathogen analysis of bacterial pneumonia secondary to influenza. Community Acquir Infect 2019;6:9-12

How to cite this URL:
Wang F, He B. Pathogen analysis of bacterial pneumonia secondary to influenza. Community Acquir Infect [serial online] 2019 [cited 2023 Jun 1];6:9-12. Available from: http://www.caijournal.com/text.asp?2019/6/2/9/286874

  Morbidity and Mortality of Bacterial Pneumonia Secondary to Influenza Top

Primary influenza virus pneumonia is relatively rare, with a mortality rate of 10%–20%. It is characterized by rapid progress and easy progression to severe pneumonia, respiratory failure, or shock within 24 h. The incidence of pneumonia caused by the mixed infection of viruses and bacteria is at least three times that of viral pneumonia, and the mortality rate is about 10%. The mortality rate of secondary bacterial pneumonia is about 7%.[1]

People's understanding of bacterial pneumonia secondary to influenza has lasted for nearly a century. The incidence of postinfluenza bacterial pneumonia varies greatly between different studies and in different regions. A research report on the autopsy of influenza deaths showed that bacteria growth could be seen on 90%–100% in >3000 lung tissue, which were all considered the presence of pneumonia.[2] An investigation of influenza during the period 1918–1919 found that the major cause of deaths was secondary bacterial pneumonia.[3] A study of hospitalized or dead patients during the influenza epidemic of 1957–1958 found that about 70%–80% of cases had bacterial pneumonia.[4],[5],[6] However, the autopsy lung tissue test results of 77 American deaths during the H1N1 epidemic in 2009 suggested that only 22% had bacterial pneumonia,[7] and another large clinical trial from California, USA, involving 1088 influenza hospitalized or dead patients, suggested that only 4% have bacterial pneumonia.[8] None of the patients (ten patients) admitted to the Michigan Hospital intensive care unit (ICU) due to H1N1 infection had a bacterial infection;[9] only 20% of 700 patients admitted to ICU in Australia and New Zealand during 2009 H1N1 epidemic was considered to have secondary bacterial pneumonia.[10] A prospective study in China during the H1N1 epidemic in 2009 showed that 55 patients with severe influenza A had pneumonia, and 22 (40%) of them had secondary bacterial infections.[11] Observed in chronological order, the proportion of bacterial pneumonia secondary to influenza had a gradual downward trend which may be due to the increase in the development and application of influenza vaccines and pneumonia vaccines in recent years with the advancement of science and technology, so the number of patients with secondary bacterial pneumonia had decreased; in addition, antibiotics available for clinical use had gradually increased, therefore some secondary bacterial infections could be controlled in time before progressing to severe illness.

  Risk Factors for Influenza Combined With Bacterial Pneumonia Top

Studies have shown that from the perspective of age distribution, infants and the elderly are more likely to have bacterial pneumonia after being infected with influenza.[12],[13] The underlying diseases of the heart and lungs are independent risk factors for the incidence of bacterial pneumonia secondary to influenza. A retrospective study showed that the rate of pregnant women hospitalized with flu or pneumonia not only increased significantly during the influenza epidemic season compared to the noninfluenza season but also the incidence was 3–4 times that of nonpregnant women.[14]

  Microbiology of Bacterial Pneumonia Secondary to Influenza Top

The earliest report of research on pathogens related to bacterial pneumonia secondary to influenza was in 1890, which found that secondary Streptococcal pneumonia caused seven patients (15.6%) to die. In the investigation of the Spanish influenza pandemic of 1918, a study involving 96 lung tissue culture from influenza death cases, suggested that bacterial infections were combined. The most common pathogens were Streptococcus pneumonia, Streptococcus pyogenes, and Staphylococcus aureus, in addition, there was a high proportion of cases with two or more bacterial infections. Investigations of influenza in London[15] and Boston[16] in the second half of the last century found that S. pneumonia was the main pathogen of secondary bacterial pneumonia, but the overall mortality rate of S. aureus infection secondary influenza was relatively higher, which was about 32%. A case study (n = 91) of an influenza that occurred in Asia between 1957 and 1958 showed that the main pathogen of secondary pneumonia was also S. pneumonia, followed by Haemophilus influenzae and S. aureus.[17] However, the autopsy analysis of 33 cases in Cleveland, USA, during the same time found that S. aureus was the main pathogenic bacteria, followed by S. pneumonia and H. influenza.[6] During the influenza pandemic in Hong Kong from 1968 to 1969, the main pathogenic bacteria associated with bacterial pneumonia were also S. pneumonia, S. pyogenes, and S. aureus.[18]

During the period 2003–2004, the investigation on the epidemic of influenza (H3N2) in the United States performed by the Centers for Disease Control and Prevention, which included laboratory-confirmed influenza patients (7550 children and 6010 adults), showed 151 children and 97 adults developed a secondary bacterial infection. About half (48%) of the adult patients required mechanical ventilation, and 17 (18%) died. The main pathogen was S. aureus; however, the S. pneumonia was the main pathogenic bacteria in children. Whether in adult or pediatric patients, the majority of S. aureus were methicillin-resistant S. aureus (MRSA).

As mentioned previously, during the H1N1 epidemic in 2009–2010, the incidence of bacterial pneumonia was relatively lower than in the past.[19],[20] Bacterial pneumonia was found in 13%–55% of the death cases.[8],[19],[21] An analysis of lung biopsies from 77 patients diagnosed with H1N1 infection showed that the most common pathogens were S. pneumonia (10 cases), S. aureus (7 cases, MRSA in 5 cases), and S. pyogenes (6 cases), Streptococcus mitis (2 cases), H. influenzae (1 case), and mixed infection (4 cases).[7]

In summary, S. pneumonia, S. aureus, S. pyogenes, and H. influenzae are more common pathogens in bacterial infection secondary to influenza. At the same time, the possibility of secondary MRSA pneumonia secondary to H1N1 should also be paid attention to in areas with high MRSA isolation.

  Pathogenesis of Bacterial Infection Secondary to Influenza Top

More and more epidemiological evidence suggested that there was synergism between influenza virus and bacteria. S. pneumonia, S. aureus, S. pyogenes, and H. influenzae, and Moraxella catarrhalis are normal parasites of the nasopharynx. In the immunocompetent host without virus infection, the above bacteria are not pathogenic.[22],[23] However, when viral infection breaks this balance, bacteria have chances to invade the downward respiratory tract. Potential mechanisms for synergism could include: viruses destruct the respiratory epithelial barrier, increase bacterial adhesion and facilitate bacteria into the blood; experimental studies demonstrate that viral neuraminidase exposes pneumococcal receptors on host cells by removing terminal sialic acids, thereby increasing bacterial adhesion and colonization; viruses can induce immunosuppression leading to bacterial susceptibility.[24]

Animal experiments have found that influenza viruses could cause neutrophils and macrophages dysfunction, excessive production of some neutrophil-independent cytokines, and activation of the immune medium, resulting in a marked increase in susceptibility to S. pneumonia and furthermore leading to more serious lung tissue damage than simple virus infection.[25] In addition, influenza virus infection could also damage bronchial ciliary power and reduce the removal of pathogenic bacteria. It is particularly worth mentioning that some studies suggested that influenza virus infection initiated a complex series of inflammatory waterfalls which involved innate-immune and acquired-immune mechanisms, and this inflammatory waterfall reaction would not disappear or stop in a short time, on the 12th day after influenza infection, the patient was still susceptible to secondary bacterial sepsis.[26],[27]

  Diagnosis and Treatment Top

Definite microbiological diagnosis is a prerequisite for targeted therapy. However, microbiological diagnosis is usually hard to make because of the limitation of test methods and materials. Obtaining sputum, respiratory aspirates, or bronchoalveolar lavage fluid depends on patients' conditions such as the severity of the disease and whether the patient can cooperate. For children, nasopharyngeal aspirates are more accurate than nasopharyngeal swabs, and the consistency of the culture of upper and lower respiratory tract specimens in children is better than in adults.[28]

With the advancement of scientific and technological methods, utilization of molecular-based pathogen panels is increasing in clinics. This method can detect multiple viruses and pathogens that are difficult to cultivate, and the detection rate is higher, and the results are obtained more quickly. However, a positive result does not necessarily indicate an active infection. Clinically, the manifestations such as cough and purulent sputum, peripheral blood white blood cell >10,000/dl, accompanied by increased neutrophil ratio, or signs of bacterial pleurisy, or even empyema, suggest that the patient has a bacterial infection.

In addition, the use of biomarkers has also significantly improved the diagnosis rate of bacterial infections. C-reactive protein and procalcitonin (PCT) are widely used clinical indicators. One study found that the sensitivity and specificity of PCT in the diagnosis of bacterial infection secondary to H1N1 were 84% and 43%, respectively, and the negative predictive value was 94% (the cutoff value is 0.29 ng/ml).[29] Accordingly, lower PCT levels seem to be a good tool for excluding secondary bacterial infection.

Based on the results of previous studies, the common pathogens of bacterial pneumonia secondary to influenza are similar to community-acquired pneumonia (CAP). Therefore, for patients with influenza suspected of secondary bacterial infection, antibiotics should be used as soon as possible. The selection of empirical antibacterial drugs can refer to the treatment guidelines of CAP and sometimes should cover MRSA.

In summary, bacterial pneumonia or lower respiratory tract infection secondary to influenza is an important cause of disease progression and increased mortality. The most common pathogens are S. pneumonia, S. pyogenes, S. aureus, and H. influenza. The mortality rate among patients with MRSA was high. In the flu season, influenza patients, especially severe patients, should be performed bacterial pathogens detection as soon as possible and give targeted treatment, which may reduce mortality and improve patient prognosis.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Metersky ML, Masterton RG, Lode H, File TM Jr., Babinchak T. Epidemiology, microbiology, and treatment considerations for bacterial pneumonia complicating influenza. Int J Infect Dis 2012;16:e321-31.  Back to cited text no. 1
Morens DM, Taubenberger JK, Fauci AS. Predominant role of bacterial pneumonia as a cause of death in pandemic influenza: Implications for pandemic influenza preparedness. J Infect Dis 2008;198:962-70.  Back to cited text no. 2
Brundage JF, Shanks GD. Deaths from bacterial pneumonia during 1918-19 influenza pandemic. Emerg Infect Dis 2008;14:1193-9.  Back to cited text no. 3
Hers JF, Masurel N, Mulder J. Bacteriology and histopathology of the respiratory tract and lungs in fatal Asian influenza. Lancet 1958;2:1141-3.  Back to cited text no. 4
Louria DB, Blumenfeld HL, Ellis JT, Kilbourne ED, Rogers DE. Studies on influenza in the pandemic of 1957–1958. II. Pulmonary complications of influenza. J Clin Invest 1959;38:213-65.  Back to cited text no. 5
Oseasohn R, Adelson L, Kaji M. Clinicopathologic study of thirty-three fatal cases of Asian influenza. N Engl J Med 1959;260:509-18.  Back to cited text no. 6
Centers for Disease Control and Prevention (CDC). Bacterial coinfections in lung tissue specimens from fatal cases of 2009 pandemic influenza A (H1N1) – United States, May – August 2009. MMWR Morb Mortal Wkly Rep 2009;58:1071-4.  Back to cited text no. 7
Louie JK, Acosta M, Winter K, Jean C, Gavali S, Schechter R, et al. Factors associated with death or hospitalization due to pandemic 2009 influenza A (H1N1) infection in California. JAMA 2009;302:1896-902.  Back to cited text no. 8
Centers for Disease Control and Prevention (CDC). Intensive-care patients with severe novel influenza A (H1N1) virus infection – Michigan, June 2009. MMWR Morb Mortal Wkly Rep 2009;58:749-52.  Back to cited text no. 9
Webb SA, Pettilä V, Seppelt I, Bellomo R, Bailey M, Cooper DJ, et al.; ANZIC Influenza Investigators. Critical care services and 2009 H1N1 influenza in Australia and New Zealand. N Engl J Med 2009;361:1925-34.  Back to cited text no. 10
Wang XJ, Jiang RM, Xu YL, Zhang W, Huangfu JK, Wang YB, et al. The analysis of the clinical features between survivors and non-survivors with the severe form of new influenza A (H1N1) viral infection. Zhonghua Jie He He Hu Xi Za Zhi 2010;33:406-10.  Back to cited text no. 11
Glezen WP. Serious morbidity and mortality associated with influenza epidemics. Epidemiol Rev 1982;4:25-44.  Back to cited text no. 12
Serfling RE, Sherman IL, Houseworth WJ. Excess pneumonia-influenza mortality by age and sex in three major influenza A2 epidemics, United States, 1957-58, 1960 and 1963. Am J Epidemiol 1967;86:433-41.  Back to cited text no. 13
Neuzil KM, Reed GW, Mitchel EF, Simonsen L, Griffin MR. Impact of influenza on acute cardiopulmonary hospitalizations in pregnant women. Am J Epidemiol 1998;148:1094-102.  Back to cited text no. 14
Scadding JG. Lung changes in influenza. QJM 1937;6:425-65.  Back to cited text no. 15
Brundage JF. Interactions between influenza and bacterial respiratory pathogens: Implications for pandemic preparedness. Lancet Infect Dis 2006;6:303-12.  Back to cited text no. 16
Petersdorf RG, Fusco JJ, Harter DH, Albrink WS. Pulmonary infections complicating Asian influenza. AMA Arch Intern Med 1959;103:262-72.  Back to cited text no. 17
Lindsay MI Jr., Herrmann EC Jr., Morrow GW Jr., Brown AL Jr. Hong Kong influenza: Clinical, microbiologic, and pathologic features in 127 cases. JAMA 1970;214:1825-32.  Back to cited text no. 18
Gill JR, Sheng ZM, Ely SF, Guinee DG, Beasley MB, Suh J, et al. Pulmonary pathologic findings of fatal 2009 pandemic influenza A/H1N1 viral infections. Arch Pathol Lab Med 2010;134:235-43.  Back to cited text no. 19
Cao B, Li XW, Mao Y, Wang J, Lu HZ, Chen YS, et al. Clinical features of the initial cases of 2009 pandemic influenza A (H1N1) virus infection in China. N Engl J Med 2009;361:2507-17.  Back to cited text no. 20
Kumar A, Zarychanski R, Pinto R, Cook DJ, Marshall J, Lacroix J, et al. Critically ill patients with 2009 influenza A (H1N1) infection in Canada. JAMA 2009;302:1872-9.  Back to cited text no. 21
Morris A, Beck JM, Schloss PD, Campbell TB, Crothers K, Curtis JL, et al. Comparison of the respiratory microbiome in healthy non-smokers and smokers. Am J Respir Crit Care Med 2013;187:1067-75.  Back to cited text no. 22
Charlson ES, Bittinger K, Haas AR, Fitzgerald AS, Frank I, Yadav A, et al. Topographical continuity of bacterial populations in the healthy human respiratory tract. Am J Respir Crit Care Med 2011;184:957-63.  Back to cited text no. 23
Peltola VT, McCullers JA. Respiratory viruses predisposing to bacterial infections: Role of neuraminidase. Pediatr Infect Dis J 2004;23:S87-97.  Back to cited text no. 24
Jason EP, Jane CD. Postviral complications: Bacterial pneumonia. Clin Chest Med 2017;38:127-38.  Back to cited text no. 25
Didierlaurent A, Goulding J, Patel S, Snelgrove R, Low L, Bebien M, et al. Sustained desensitization to bacterial Toll-like receptor ligands after resolution of respiratory influenza infection. J Exp Med 2008;205:323-9.  Back to cited text no. 26
Hussell T, Cavanagh MM. The innate immune rheostat: Influence on lung inflammatory disease and secondary bacterial pneumonia. Biochem Soc Trans 2009;37:811-3.  Back to cited text no. 27
Jartti T, Söderlund-Venermo M, Hedman K, Ruuskanen O, Mäkelä MJ. New molecular virus detection methods and their clinical value in lower respiratory tract infections in children. Paediatr Respir Rev 2013;14:38-45.  Back to cited text no. 28
Rodríguez AH, Avilés-Jurado FX, Díaz E, Schuetz P, Trefler SI, Solé-Violán J, et al. Procalcitonin (PCT) levels for ruling-out bacterial coinfection in ICU patients with influenza: A CHAID decision-tree analysis. J Infect 2016;72:143-51.  Back to cited text no. 29


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