Lower Respiratory Tract Infection (Pneumonia) - Chapter 2

3 July, 2023

Epidemiology of CAP: For the past 10 years, we are able to do microbiology diagnosis better. So, we can see mixed infection; we can see more atypical agents, for example, Legionella, Mycoplasma, and Chlamydia pneumoniae. However, the most common causative agent of CAP is still Streptococcus pneumoniae. All over Thailand or any country in Southeast Asia, Streptococcus pneumoniae, we see in around >50%. And we also now see increased incidence of atypical Legionella, Mycoplasma, and Chlamydia. The big difference is Staphylococcus aureus, which is quite common in the US and in some European countries. But in Southeast Asia, particularly in Thailand, we rarely see pneumonia due to Staph aureus. So even MRSA is very rare in community-acquired pneumonia. And even in hospital-acquired pneumonia, we rarely see MRSA. We are now seeing more drug-resistant bacteria in CAP due to many, many confounders or many risk factors. So how to get the appropriate treatment at the beginning? From many studies, we see risk factors for drug resistance; pathogens help us a lot in choosing empiric antibiotics.

Number one, in the patients who have a history of previous colonization, with some resistant bacteria, for example, Pseudomonas aeruginosa or MRSA. And secondly, patients who live or stay in the healthcare environment for the past 90 days, for example, prior hospitalization, people from nursing homes, people who have been in the intensive care unit recently, people who came to the hospital many times for wound care, chronic hemodialysis, or, in some areas, patients who are on home intravenous antibiotic therapy or opioid therapy in some private hospitals in Thailand as well. And also, another risk factor for multidrug-resistant pathogens is the host factor. As I mentioned earlier, immunosuppression,  cerebrovascular accident (CVA), and particularly those who have chronic lung disease, for example, COPD, chronic respiratory disease, and bronchiectasis, or some systemic disease like diabetes, will carry risk factors for resistant pathogens. And another specific drug or treatment, for example are patients who have been on steroids or immunosuppressive drugs or patients who undergo tube feeding, particularly nasogastric tube feeding, carry more multidrug-resistant pathogens.

As I have shown in the previous slide – more than 50% of Strep pneumoniae is the leading cause of CAP in many countries. So, they use another study from 11 Asian countries done from March 2008 to December 2009. You can see here, in China, Hong Kong, India, South Korea, Malaysia, Sri Lanka, Vietnam, and Thailand, the increasing incidence of drug resistant Strep pneumoniae (DRSP), particularly to penicillin, but as we know with penicillin, you can give a higher dose. So, we have to differentiate non-meningeal isolate and meningeal isolate. So, I already told you about a non-meningeal isolate. You see here in Thailand, the MIC90 of Strep pneumoniae is 2; that means, we have to give a higher penicillin dose or we have to give a higher amoxicillin dose – more than 2 g/day. And also, for erythromycin, from here, the resistance rate in Strep pneumoniae is up to 44.3%. So, we cannot use erythromycin to treat CAP. But we still can use advanced macrolide, for example, erythromycin for the treatment of CAP in some settings. And for levofloxacin, the resistance is really low in Thailand and also in other Asian countries.

And this is our National data from 83 hospitals in Thailand, from all over the country. You can see from the year 2000 to 2021. For penicillin, in the testing we used oxacillin. You can see that penicillin resistance is high, up to 52% in 2010, which dropped down a little bit to 40% in the year 2019. Anyway, we still can use a higher penicillin dose or a higher amoxicillin dose for the treatment of CAP due to Streptococcus pneumonia.

And see here, levofloxacin, from the year 2000 to the year 2021. The resistance rates remain low. One factor is, at the beginning, we use 500 mg daily levofloxacin, and right now, we use 750 mg daily levofloxacin. And also, with the good pharmacokinetic/pharmacodynamic (PK/PD) of levofloxacin, the resistance rate remains low, as you see here, in 20 years.

Also in some settings, as these people live longer, we can see Pseudomonas aeruginosa in CAP in some settings in those with risk factors, in those with chronic kidney disease or diabetic patients. So, I am going to show you also the Pseudomonas aeruginosa resistance rate in Thailand, from the same hospital up to the year 2021. For Pseudomonas aeruginosa, the best antibiotic right now is polymyxin or colistin, but this antibiotic is so nephrotoxic. So, usually, if we have other medicine, we will not use colistin. The second-best antibiotic is amikacin. The resistance rate is only 5%–8%. So, from time to time, when we deal with Pseudomonas aeruginosa pneumonia, as one antibiotic in the combination treatment, most doctors will add amikacin for the first few days. And another good medicine for Pseudomonas aeruginosa is piperacillin/tazobactam. You can see now, the resistance rate was about less than 10% before, but for the past 2 years, the incidence is a little bit increased to 11%–14%. So, now we have come across MDR Pseudomonas aeruginosa in Thailand as well.