Detection of Atypical Pathogens in Community Acquired Pneumonia by Indirect Immunofluorescence Assay

Abstract

Introduction: Community Acquired Pneumonia (CAP), as the name suggests, is acquired at the community level, and symptoms usually develop within 48 hours. There are two types of CAP, namely, typical and atypical. Typical pneumonia is usually caused by bacteria such as Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. Atypical pneumonia is caused by Mycoplasma pneumoniae, Chlamydophila pneumoniae, Legionella pneumophila, and Coxiella burnetii, as well as respiratory viruses, such as Adenovirus, Respiratory Syncytial Virus (RSV), Influenza viruses A and B, and Parainfluenza viruses 1,2,3, among others. Typical and atypical CAP can be distinguished by the absence or presence of extrapulmonary symptoms. Aim: To elucidate the proportion of atypical respiratory pathogens that cause CAP in a tertiary care hospital setting. Materials and Methods: This was a cross-sectional study that was conducted at the Department of Medicine, Chest Medicine and Microbiology of MS Ramaiah Medical College, Bengaluru, Karnataka, India. The study included 202 patients, aged 18 years and above with clinical and radiological features of CAP. Indirect Immunofluorescence Assay (IFA) was carried out to detect the pathogens. Results: The prevalence of atypical pathogens was 33.17% among all CAP patients. Atypical pneumonia was more prevalent in males and in the age group of >61 years. The most common pathogens included Mycoplasma pneumoniae (12.38%) followed by Legionella pneumophila (9.90%) and influenza A (5.94%). Typical pneumonia was primarily caused by Streptococcus pneumoniae (9.9%), followed by Klebsiella pneumoniae (1.49%), Staphylococcus aureus (1.49%), and Haemophilus influenzae (0.49%). Mixed infections occurred in 16 patients. Conclusion: Active screening for CAP is needed in all wards and Intensive Care Units (ICU), as more patients with CAP are increasingly being admitted to ICU. Data on the proportion of atypical CAP will help to use antibiotics prudently for a better prognosis, thereby preventing the emergence of antibiotic resistance.