Epidemiology, aetiology, and management of community-acquired pneumonia (CAP) in Hong Kong

19 November, 2020

Dr LAM Bing
Director, Respiratory Medicine Centre
Hong Kong Sanatorium Hospital
Hong Kong

In Asia, community-acquired pneumonia (CAP) causes almost one million deaths in adults annually.¹ Streptococcus pneumoniae is one of the most commonly identified causative pathogens; the disease burden of pneumococcal infections remains alarming due to widespread emergence of antimicrobial resistance in many countries worldwide.²

Dr Lam Bing – Director of the Respiratory Medicine Centre at the Hong Kong Sanatorium Hospital – shares insights on the management of CAP caused by S. pneumoniae and atypical pathogens.

Q1. Please describe the aetiology and epidemiology profiles of CAP in Hong Kong.

There is currently no large-scale study to investigate the most common pathogens causing CAP in Hong Kong. However, the trends in Hong Kong should be similar to other countries; although the causative pathogens may not be identified in at least half of the pneumonia cases, we assume that the majority of cases are caused by Streptococcus pneumoniae and a quarter of cases associated with atypical pathogens. It is also possible to isolate both S. pneumoniae and atypical in clinical samples at the same time.

Q2. Previous reports have documented high prevalence rates of macrolide resistance among S. pneumoniae isolates in Asian countries.² What is the local prevalence of macrolide-resistant S. pneumoniae and atypical pathogens in patients with CAP?

The Infectious Disease Society of America (IDSA) recommends the macrolide azithromycin as first-line treatment for CAP. However, we do not follow this recommendation in Hong Kong because local studies conducted 20–30 years ago have shown that more than 60% of S. pneumoniae are resistant to clarithromycin and 40% isolates are resistant to azithromycin. As such, clinicians do not use macrolide alone for the treatment of CAP; however, macrolide should be added as a combination therapy to cover atypical pathogens. Beta-lactam/beta-lactamase inhibitors are recommended instead.

Q3. What are the next steps after treatment failure with macrolides?

Clinical improvement is expected within 48 hours of antibiotic administration. When patients do not improve after two days of antibiotic treatment, clinicians should consider whether the current regimen covers the causative pathogens or whether it is a bacterial infection or other pneumonia-like illnesses. Therefore, it is important to review the effectiveness of current treatment. For instance, if patients do not improve on beta-lactam/beta-lactamase inhibitor plus macrolide after two days of treatment initiation, clinicians should consider whether the infection is caused by antimicrobial pathogens such as Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus (MRSA) or macrolide-resistant atypical pathogen – and modify the antibiotic regimen accordingly. Clinicians should consider switching to a broad-spectrum antibiotic to cover multidrug-resistant (MDR) pathogens or a different antibiotic class to cover macrolide-resistant atypical pathogens.

Q4. What measures have been adopted to curb the emergence of antibacterial-resistant pathogens?

Frankly speaking, there is only a 50% possibility of identifying the causative pathogen from blood, urine or sputum culture before the initiation of antibiotics. For instance, although we may be able to isolate bacteria in a sputum sample, the isolates may potentially be colonising bacteria of the upper airways. As such, we do not await culture results before initiating antibiotics because empiric antibiotics given within four hours of disease onset can greatly decrease mortality. The switch of antibiotic treatment should be based on clinical judgement until rapid tests with quick turnaround time such as polymerase chain reaction (PCR) tests are available in the future to confirm the presence of drug-resistant pathogens.

The guidelines should be followed closely in the presence of MDR pathogens – which is not a major concern in CAP currently. However, clinicians should be cautious in managing patients who live in nursing homes, those who are frequently rehospitalised, those who have frequent hospital visits (e.g., patients requiring dialysis) or patients who have received antibiotic treatment within the last three months – these group of patients are more likely to have MDR infections. The antibiotic regimen for these patients should be individualised based on their conditions. For instance, first-line treatment with fluoroquinolones can be considered in patients with penicillin allergy as fluoroquinolones have a broad coverage of both typical and atypical pathogens.

Q5. One of the major concerns of empirical fluoroquinolones use for CAP is the masking of tuberculosis (TB).³ What approach do you take when managing TB patients presenting with CAP?

TB is prevalent in Southeast Asia including Hong Kong – we are still reporting 40–50 cases per 100,000 population annually. Fluoroquinolones are effective for the treatment of TB and are used for the treatment of patients with TB presenting as CAP. However, the use of fluoroquinolones is not recommended as first-line treatment for CAP unless TB has been ruled out. Serum procalcitonin (PCT) is a useful biomarker to distinguish between bacterial infections and non-bacterial infection (including TB) – once TB is ruled out, patients can be treated with first-line fluoroquinolones. Serum PCT levels can also be used as a real-time monitoring of patient’s condition after antibiotics initiation. In fact, there are several studies which use PCT to guide antibiotic treatment duration. The duration of treatment for uncomplicated CAP is between 5–7 days whereas in severe cases, treatment duration is usually between 10–14 days. However, with the availability of PCT results, clinicians can confidently stop antibiotics when PCT level is low – and this has been shown to reduce the duration of antibiotic treatment, leading to reduced cost of treatment as well as preventing the emergence of antibiotic-resistant pathogens.

Q6. How is the management of pneumonia patients different in the current COVID-19 pandemic?

The most common causative pathogen in CAP is S. pneumoniae whereas in post-influenza pneumonia, the most common pathogens are S. pneumoniae and S. aureus – with the emergence MRSA being a major concern. Therefore, when patients with pneumonia after flu-like symptoms, clinicians should consider whether this is a case of viral or bacterial pneumonia. Clinicians can then streamline antibiotics if MRSA is ruled out in the case of bacterial pneumonia.

In the case of COVID-19 infection, pneumonia develops when the defensive mechanism of the upper airways is impaired, resulting in the invasion of the lower respiratory tract by the colonising bacteria of the upper airways. Therefore, it is not uncommon for patients with COVID-19 to have secondary bacterial pneumonia. These patients are typically prescribed antibiotics. In my opinion, antibiotic should be prescribed if serum PCT level is elevated. As mentioned, antibiotics treatment should cover MRSA post-influenza. We are uncertain about the causative agents of bacterial pneumonia post-COVID-19 – nevertheless, appropriate antibiotics should be used in the case of bacterial infections to improve patient outcomes.

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