Discussion and Conclusion
The novel coronavirus has been found to have membrane glycoprotein,
spike protein, nucleocapsid protein, envelope protein and coagulase[5]. The spike glycoprotein on the surface of the
virus plays a major role in its attachment and entry into host cells,
and the infection can lead to lethal damage in the lungs, heart,
kidneys, circulatory system, gastrointestinal tract and nervous system
tissues [6]. Elderly people are particularly
vulnerable to the virus due to their weakened immune systems, and
evidence suggests that a large number of hospitalized patients during
the COVID-19 pandemic had mixed bacterial infections and secondary
bacterial infections, which were a major cause of higher mortality in
elderly patients [7]. When the novel coronavirus
invades the lungs, it causes damage to the lung cells and tissues, which
attracts neutrophils and macrophages to the infected site and promotes
inflammation, and eventually leads to bacterial adhesion and invasion
into the cells and proliferation [8]. Therefore,
it is essential to identify the bacterial pathogens of LRTIs in the
elderly.
The results of this study showed that Klebsiella
pneumoniae,Pseudomonas aeruginosa, Bacteroides fragilis, Escherichia
coli, Stenotrophomonas maltophilia, Staphylococcus aureus, andStreptococcus pneumoniae were the main pathogenic bacteria in the
sputum specimens of 163 hospitalized elderly patients in this study.
This is consistent with similar studies [9], which
showed that the common bacteria identified in respiratory cultures, even
the sputum culture results of elderly patients with pulmonary
infections, were mostly Gram-negative bacteria, mainly includingKlebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa,
Bacteroides fragilis, etc.; the Gram-positive bacteria infected
included Streptococcus pneumoniae, Staphylococcus aureus , etc.Klebsiella pneumoniae is a Gram-negative bacteria with a thick
capsule, mostly distributed in the human respiratory and
gastrointestinal tracts, and is a common pathogen for elderly
respiratory infections. SAIDK et al. [10]conducted a screening for combined microbial infection in 301 COVID-19
patients, and the main microorganisms detected were Klebsiella
pneumoniae (37%, 48/301), Pseudomonas aeruginosa (8.5%,
11/301), and Escherichia coli (18.6%, 24/301).
The opportunistic Gram-negative bacillus Stenotrophomonas
maltophilia is known to infect mostly elderly patients. According to
one study, individuals over the age of 60 were more prone to S.
maltophilia infection, which could be attributed to immunosuppression[11]. In recent years, S. maltophilia has
been relatively stable in third place among non-fermenting Gram-negative
bacteria, after Pseudomonas aeruginosa and Acinetobacter
baumannii, according to the CHINET monitoring
service[12]. Patients with severely impaired or
weakened immune functions were more susceptible to serious consequences
when infected with S. maltophilia, suggesting that the
respiratory tract was the main site of colonization and infection ofS. maltophilia , which may have been associated with its ability
to form biofilms and colonize the respiratory tract of hospitalized
patients [13]. Recently, S. maltophilia was
reported as one of the secondary bacterial infections in ICU patients
with COVID-19 [9], which is similar to what was
found in this study: the infection rate of S. maltophilia was
higher in the COVID-19 group than in the CNT group.
Acinetobacter baumannii is a Gram-negative bacterium with strong
vitality, and it is a major opportunistic pathogen that can cause double
infection, especially in hospitalized patients with viral respiratory
infection [14]. Recent studies have shown that the
infection rate of Acinetobacter baumannii in COVID-19 patients
varies widely in different regions. For example, Nanshan Chen et al.[15] reported that among 99 COVID-19 patients in
Wuhan, only one was cultured with Acinetobacter baumannii , with
an infection rate of 10.1% (1/99); another domestic report showed that
among 1495 hospitalized COVID-19 patients in Wuhan, 102 (6.8%) had
bacterial mixed infection, mainly Acinetobacter baumannii(35.8%), and nearly half (49.0%, 50/102) died during hospitalization[16]; Iranian scholars SHARIFIPOUR et al.[14] reported that 17 out of 19 elderly COVID-19
patients had Acinetobacter baumannii infection, with an infection
rate of 89.5% (17/19); Brazilian researchers SILVADL et al.[17] reported that the infection rate ofAcinetobacter baumannii was 32.8% (21/64); SAIDKB et al. in
Saudi Arabia reported [10] that 34 of the 301
COVID-19 patients had drug-resistant Acinetobacter baumannii(26%, n=34).
The infection rate of Acinetobacter baumannii varies in different
regions, and further research is needed to investigate the specific
reasons. In the hospital environment, COVID-19 elderly LRTIs patients
may face another threat to health, which is mixed bacterial infection
and nosocomial secondary bacterial infection, especially the mixed
infection and secondary infection of Staphylococcus aureus andAcinetobacter baumannii , which may seriously affect the clinical
outcome of COVID-19 patients.
Whereas, This study has certain limitations, for it was solely focused
on bacteria, not including fungi, mycoplasma, chlamydia, parasites and
other viruses into the study of pathogens in elderly LRTIs patients; The
number of patients enrolled is small, which could result in a sample
size bias ,therefore large-scale clinical studies need to be conducted
to investigate the incidence, prevalence, characteristics and
microbiological distribution of COVID-19 complicated infections. As a
result, a multicenter, prospective, longitudinal study is required to
confirmed the research.
In conclusion, the current study has identified the main bacterial
pathogens of elderly LRTIs patients, and has highlighted the importance
of identifying and treating secondary bacterial infections in elderly
patients with COVID-19. Furthermore, the findings of this study suggest
that Klebsiella pneumoniae, Pseudomonas aeruginosa, Bacteroides
fragilis, Escherichia coli, Stenotrophomonas maltophilia, Staphylococcus
aureus, and Streptococcus pneumoniae are the main bacterial
pathogens of elderly LRTIs patients, and that Stenotrophomonas
maltophilia is an opportunistic pathogen that is particularly dangerous
for elderly patients with weakened immune systems.