Pneumonia is defined as an acute respiratory illness associated with recently developed radiological pulmonary shadowing which may be segmental, lobar or multi-lobar1. Community acquired pneumonia (CAP) is defined as pneumonia acquired outside the hospital by an immune-competent individual. It is to be distinguished, on the basis of a wider spectrum of pathogens, from nosocomial pneumonia (which arises more than 48 hours after hospital admission or within 3 months of discharge) and from pneumonia in an immune-compromised host (e.g., in the setting of neutropenia, iatrogenic immune-suppression with drugs, status post organ or stem-cell transplantation, HIV infection, or a congenital immune deficiency2.
Underlying diseases (Chronic obstructive pulmonary disease, compromised immune system, dementia, gastro esophageal reflux disease, etc.) increase susceptibility of the patients for pneumonia3. Alternatively, habitual pathogens could show particular patterns of antimicrobial resistance4. Undoubtedly the knowledge of these microbiological characteristics is critical and represents the basis for empirical treatments. Serious co-existing illness has been identified as modifying factors of severity of pneumonia5. On the basis of these appreciation, published guidelines on pneumonia advocate specific criteria for antibiotic selection and the management of patients in the presence of co-morbid diseases6.
As the etiology of CAP varies geographically the understanding of local epidemiology may play an important role in making proper empirical treatment choices before laboratory test results are available. This is especially true for Bangladesh and other developing countries where healthcare systems operate on poor hygiene system and lack proper facilities to contain infections. In these countries, early treatment is usually based on the patient’s clinical symptoms rather than diagnostic results. Therefore, patient’s early prognosis to final outcome might be much improved by available epidemiologic data for the most frequently isolated pathogenic organisms7. However, such complete data is scarce in Chittagong, Bangladesh.
There is a need to conduct regular prevalence and antibiogram studies to develop empirical guidelines for treatment of CAP in that particular region. The hospital antibiogram is a periodic summary of antimicrobial susceptibilities of local bacterial isolates submitted to the hospital's clinical microbiology laboratory. Antibiograms are often used by clinicians to assess local susceptibility rates, as an aid in selecting empiric antibiotic therapy, and in monitoring resistance trends over time within an institution. Antibiograms can also used to compare susceptibility rates across institutions and track resistance trends8.
On the other hand, antimicrobial resistance is a well-known important emerging clinical and public health problem. Controlling antimicrobial resistance is a major issue confronting organized health care today. The irrational use of antibiotics has an influence in the spread of antimicrobial resistance among bacteria9. Both under-use and over-use of broad spectrum antibiotics for an infection as common as CAP could be harmful, particularly in Asia where mortality is high, resources scarce and antibiotic resistance an increasing problem10.
National data on incidence, etiology and mortality of CAP is not available in Bangladesh. Pneumonia’s mortality is highly correlated with socio-economic factors and is a far less frequent cause of death in high-income countries. It occurs about five times more frequently in the developing world than the developed world. The incidence of CAP ranged from 4 million to 5 million cases per year, with about 25% requiring hospitalization11. Death rates in hospital admitted patients are between 5-10% but may be as high as 50% in severe illness1. The annual incidence of CAP in Europe is 1.6-10.6/1,000 adults12. In Asia, CAP causes an estimated one million adult deaths per year (160,000 cases per year among those aged 15-59 years)7.
CAP is a frequent cause of antibiotic prescription, either in hospital or in the ambulatory setting. Antibiotics prescribed for CAP exert a selection pressure favoring the emergence of multidrug resistant bacteria, not only on lung pathogens (like S. pneumoniae or M. pneumoniae), but also on bacteria colonizing the skin or the gastrointestinal tract, like Staphylococcus aureus or enterobacteriaceae. The emergence of methicillin-resistant S. aureus, and lately of extended spectrum betalactamase (ESBL)-producing enterobacteriaceae, are worrying consequences of widespread antibiotic use. A high correlation is present between the prevalence of S. pneumoniae resistance towards diverse antibiotic classes and the density of prescription of the same antibiotic classes. On an individual level, one-time antibiotic administration enhances the prevalence of colonization by resistant bacteria up to one year13.
In CAP, in approximately 6% of the cases a MDR pathogen is involved, the most frequent described being S. aureus and P. aeruginosa. A study by Aliberti et al. reported that MDR microorganisms were involved in 3.3% to 7.6% CAP cases in which the most commonly identified MDR pathogen was methicillin-resistant S. aureus (MRSA). Community-acquired methicillin-resistant S. aureus (CA-MRSA) has become an important CAP pathogen in endemic areas in Europe14. Since the recommendation of current international guidelines for severe CAP is empiric therapy with β-lactam with macrolide or fluoroquinolone, which may not provide adequate protection against MRSA, microbiological diagnosis of these cases is very important11.
To get updated information for proper therapeutic interventions, periodic evaluation and regional surveillance programs is necessary for the development local data about the antimicrobial sensitivity to respiratory pathogens for CAP. In this study, we aimed to identify the common bacterial pathogens in hospitalized patients with CAP from Chittagong, Bangladesh. We also determined pathogens’ antibiotic susceptibility patterns to evaluate the changing trend of antimicrobial susceptibility in this region. Meanwhile the short term clinical outcomeof antibiotic therapy for CAP during hospital stay was also observed.
Though hospitalization of adult patients with CAP are increasing in Bangladesh, information regarding their clinical presentation, microbiological characteristics, antimicrobial susceptibility pattern that is required for choosing empiric antibiotic treatment and outcome of patients are lacking. Microorganisms causing CAP vary in their susceptibility to antimicrobials from place to place and time to time. CMCH is the 2nd largest tertiary care hospital in Bangladesh and a referral centre to the hospitals in the surrounding districts. Up to date knowledge of the microbial organisms and antibiotic susceptibility pattern of patients with CAP is essential for defining empirical treatment. There is a paucity of recent study regarding these issues in Bangladesh especially in peripheral hospital settings, where a large number of CAP patients with different comorbidities are managed routinely.