We conducted a retrospective descriptive study to describe the number of health care-associated infections and the resistance patterns of isolated microorganisms in patients with severe COVID-19 admitted to the Intensive Care Unit at a tertiary medical center in the State of Mexico. Generalized empirical antimicrobial prescriptions of beta-lactams as third-generation cephalosporins were found, among which ceftazidime and ceftriaxone stood out, as well as a treatment with the fluoroquinolone levofloxacin, both antibacterial treatments administered simultaneously from admission to the ICU. In our study, initially 100% of the study patients and those who did not enter the study due to exclusion criteria had the aforementioned prophylactic antimicrobial therapy, something that contrasts with a study carried out by Vaughn et al., Who reported the use of empirical antibiotics in 56.6% of COVID-19 patients admitted to 38 Michigan hospitals. In that study, empirical use of antibiotics ranged from 27–84% among hospitals, and the most frequently prescribed antibiotic was ceftriaxone in 38.9%. Although the prevalence of bacterial coinfections on admission is low (2.4-7%), empirical antimicrobial treatment is extremely common (72–90%).15 Taking into account the amount of bacterial coinfections in patients with the disease of the COVID-19 so low, the World Health Organization suggested not using antibiotics to treat the disease.16
On the other hand, the use of levofloxacin is justified as an initial treatment for nosocomial pneumonia or community-acquired pneumonia due to its wide spectrum and good concentration achieved in the lungs,17 as well as the use of third-generation cephalosporins such as ceftriaxone at a dose of 1 and 2 g.18 However, when presenting a co-infection of bacterial etiology, I modify the treatment to a targeted therapy in most cases, this prophylactic treatment was used for 7 to 10 days according to the results of the cultures performed., where antimicrobial therapy had to be scaled to carbapenemics, colistin, vancomycin or linezolid, according to the isolated microorganisms.
However, resistance to antibiotics suggests that bacteria already have resistance to most of the drugs of each of the antimicrobial families19 and that it gives them a classification of Extremely Drug Resistant, of which there are 84 strains and Multi Drug Resistant with 12 strains.
In a study by Li J et al. A total of 159 strains of bacteria were isolated from the cultures in the 102 patients. Among the isolated bacteria, Gram negative bacteria were the main bacteria, representing 85.5%. The three main bacteria were Acinetobacter baumannii (A. baumannii, 35.8%), Klebsiella pneumoniae (K. pneumoniae, 30.8%), and Stenotrophomonas maltophilia (S. maltophilia, 6.3%)20 While in our study, the Gram positive bacterium S. aureus represents a total of 38% of the isolates and 100% in resistance to methicillin by the oxacillin test and the cefoxitin test. On the other hand, in Gram negative isolates, P. aeruginosa with 23% and S. maltophilia with 20% of the total of the isolates were the ones that had the highest frequency in the total of samples. A baumannii, which in Li's study was the most isolated bacterium in our study, represents only 5% of the isolates.
Only 79% of bacteria isolated by co-infection correspond to pneumonia associated with mechanical ventilation or associated with health care, while 21% correspond to infections of the pleural fluid, catheter infections, bacteremia and urinary tract infections.
A high number of strains resistant to beta-lactams are observed, both for penicillin and its derivatives with 100%, penicillin derivatives with beta-lactamase inhibitor such as ampicillin / sulbactam, amoxicillin / clavulanic acid, piperacillin / tazobactam, also with a resistance of 100%. In the case of first, second, third and fourth generation cephalosporins, 100% resistance is observed, except for ceftazidime, which presents resistance of only 96.3% thanks to the susceptible strains of S. maltophilia. For ESBL-producing strains, high resistance to penicillins and cephalosporins is expected due to their enzymatic activity21, for the case of carbapenemase-producing strains they also explain the high resistance index to beta-lactams22 already mentioned as well as the carbapenemics meropenem, ertapenem and imipinem resistance of 83.9%, 93.5% and 89.7% respectively. The strains with the highest production of carbapenemases in this study are P. aeruginosa XDR and A. baumannii XDR. In the case of high levels of resistance to all beta-lactams for S. aureus, it is explained by resistance to methicillin, which implies not an enzyme but the modification of the PBP Penicillin-Binding Proteins that confers resistance to all beta-lactams.23
Quinolone resistance is caused by various mechanisms, particularly plasmid-ediated quinolone resistance (PMQR) which contains the pentapeptide repeat family Qnr proteins (QnrA, QnrB, QnrS, QnrC, and QnrD). These proteins confer quinolone resistance by physically protecting DNA gyrase and topoisomerase IV from quinolone acts. This condition may provide a selective advantage for the development of quinolone resistance which could result in therapeutic failure.24 Quinolone resistance is more common in Enterobacteriaceae that show resistance to beta-lactams due to the production of extended-spectrum beta-lactamases (ESBL), acquired class C beta-lactamases or carbapenemases.25
One of the great limitations in the study was not having the means to carry out a detailed characterization at the molecular level of the different carbapenemases expressed by the isolated MDR and XDR organisms, as well as the ESBL of the producing strains, which would allow us to know the mechanisms exact resistance of the antibiotics used in the antibiogram and give a correct directed therapy.
Another limiting point of the present study is the lack of manual and automated phenotypic and genotypic tests for the detection of colistin resistance, for which reason the absence of PDR-resistant Pan Drug-resistant bacteria cannot be assured, since they were not considered in the present study. But some of the Pseudomonas aeruginosa and Acinetobacter baumannii cultures after colistin treatment persisted in subsequent control cultures. Which indicates possible mechanisms of resistance to the last line of treatment.
In this study, the targeted therapies used for the treatment of isolated bacteria are not mentioned, due to a later study that is intended to report to indicate resistance patterns in late-line drugs for the isolates obtained and the therapeutic successes or failures, in addition to the considerations that are taken into account in the choice of medication.
As an analysis of the logistic regression we have the following. Finding that having a previous NCD such as type 2 diabetes mellitus, hypertension or ischemic disease increases the risk by 10,345 (IC 1,127 − 94,995) (times more likely to develop E. Coli.
On the other hand, analyzing the factors that are associated for the development of infection by A. baumannii, being a man increases by 19,650 (IC 1,187–325,389) the probability of acquiring the disease compared to being a woman, as well as having positive smoking increases the risk in 31,582 (CI 1,469–679,621) times with respect to those who do not smoke, being statistically significant in both cases.
For the case of other bacteria (E. clocae, S. epidermidis, S. haemolyticus, E. faecalis) the body weight classified as normal weight, overweight and obesity was analyzed. Finding that having a normal weight reduces the risk of developing a bacterial pathology by 12,345 (IC 0.009–0.760) compared to those who are overweight or obese