The incidence and aetiology of hospitalised community-acquired pneumonia among Vietnamese adults: a prospective surveillance in Central Vietnam

Abstract

Background: Lower respiratory tract infection (LRTI) including Community-acquired pneumonia (CAP) is a common infectious disease that is associated with significant morbidity and mortality. The patterns of aetiological pathogens differ by region and country. Special attention must be paid to CAP in Southeast Asia (SEA), a region facing rapid demographic transition. Estimates burden and aetiological patterns of CAP are essential for the clinical and public health management. The purposes of the study are to determine the incidence, aetiological pathogens, clinical pictures and risk factors of community-acquired pneumonia (CAP) in the Vietnamese adult population.

Methods: A prospective surveillance for hospitalised adult CAP was conducted in Khanh Hoa Province, Central Vietnam. All adults aged ≥15 years with lower respiratory tract infections (LRTI) admitted to a provincial hospital from September 2009 to August 2010 were enrolled in the study. Patients were classified into CAP and non-pneumonic LRTI (NPLRTI) according to the radiological findings. Bacterial pathogens were identified from sputum samples by the conventional culture and polymerase chain reaction (PCR) for Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis; 13 respiratory viruses were identified from nasopharyngeal specimens by PCR.

Results: Of all 367 LRTI episodes examined, 174 (47%) were CAP. Older age, the presence of underlying respiratory conditions, and higher index score of smoking were associated with CAP. The one-year estimated incidence of hospitalised adult CAP in our study population was 0.81 per 1,000 person years. The incidence increased considerably with age and was highest among the elderly. The case fatality proportion of hospitalised CAP patients was 9.8%. Among 286 sputum samples tested for bacterial PCR, 79 (28%) were positive for H. influenzae, and 65 (23%) were positive for S. pneumoniae. Among 357 samples tested for viral PCR, 73 (21%) were positive for respiratory viruses; influenza A (n = 32, 9%) was the most common.

Conclusions: The current adult CAP incidence in Vietnam was relatively low; this result was mainly attributed to the young age of our study population.

Figure 1

Flow chart of case enrolment and allocation. ICD-10; International Classification of Diseases, 10th revision. Left branch indicates active surveillance based on admission diagnosis of LRTI and 46 cases were excluded. Numbers of patients living in Nha Trang were used to calculate incidence of pneumonia. Right branch shows retrospective surveillance based on discharge diagnosis.

Figure 2

The incidence of hospitalised pneumonia per 1,000 persons by age group and gender. Incidence among male population were showed in solid line and those among female population were showed in dashed line. 95% confidence interval of each points were showed in vertical lines.

Figure 3

The proportion of viral and bacterial agents identified from the enrolled patients by age group. Pathogens detected in sputum and/or nasopharyngeal swabs of patients with LRTI. Patients of 15 to 64 years old were presented in left (A) and those over 65 years old were presented right (B).

Figure 4

The monthly incidence of CAP amongst elderly ≥ 65 years and young adult 15–64 years and number of 2009pH1N1 influenza infections. The 2009pH1N1 season was defined between September 2009 and December 2009. The bars indicate number of 2009pH1N1 detected in our study. The estimated monthly incidences per 100,000 population amongst elderlies ≥ 65 years old were showed in solid line, those amongst young adults in dashed line.

Figure 5

The predicted number of adult CAP patients in Vietnam in 2009, 2020, and 2030. The age-group specific number of CAP patients was estimated using the predicted population number [7] and our age group-specific incidence estimates.