Somrak Chantra

Incidence, Seasonality and Mortality Associated with Influenza Pneumonia in Thailand: 2005–2008

Background Data on the incidence, seasonality and mortality associated with influenza in subtropical low and middle income countries are limited. Prospective data from multiple years are needed to develop vaccine policy and treatment guidelines, and improve pandemic preparedness. Methods During January 2005 through December 2008, we used an active, population-based surveillance system to prospectively identify hospitalized pneumonia cases with influenza confirmed by reverse transcriptase–polymerase chain reaction or cell culture in 20 hospitals in two provinces in Thailand. Age-specific incidence was calculated and extrapolated to estimate national annual influenza pneumonia hospital admissions and in-hospital deaths. Results Influenza was identified in 1,346 (10.4%) of pneumonia patients of all ages, and 10 influenza pneumonia patients died while in the hospital. 702 (52%) influenza pneumonia patients were less than 15 years of age. The average annual incidence of influenza pneumonia was greatest in children less than 5 years of age (236 per 100,000) and in those age 75 or older (375 per 100,000). During 2005, 2006 and 2008 influenza A virus detection among pneumonia cases peaked during June through October. In 2007 a sharp increase was observed during the months of January through April. Influenza B virus infections did not demonstrate a consistent seasonal pattern. Influenza pneumonia incidence was high in 2005, a year when influenza A(H3N2) subtype virus strains predominated, low in 2006 when A(H1N1) viruses were more common, moderate in 2007 when H3N2 and influenza B co-predominated, and high again in 2008 when influenza B viruses were most common. During 2005–2008, influenza pneumonia resulted in an estimated annual average 36,413 hospital admissions and 322 in-hospital pneumonia deaths in Thailand. Conclusion Influenza virus infection is an important cause of hospitalized pneumonia in Thailand. Young children and the elderly are most affected and in-hospital deaths are more common than previously appreciated. Influenza occurs year-round and tends to follow a bimodal seasonal pattern with substantial variability. The disease burden varies significantly from year to year. Our findings support a recent Thailand Ministry of Public Health (MOPH) decision to extend annual influenza vaccination to older adults and suggest that children should also be targeted for routine vaccination.

Human Rhinovirus Infections in Rural Thailand: Epidemiological Evidence for Rhinovirus as Both Pathogen and Bystander

Background We describe human rhinovirus (HRV) detections in SaKaeo province, Thailand. Methods From September 1, 2003–August 31, 2005, we tested hospitalized patients with acute lower respiratory illness and outpatient controls without fever or respiratory symptoms for HRVs with polymerase chain reaction and molecularly-typed select HRVs. We compared HRV detection among hospitalized patients and controls and estimated enrollment adjusted incidence. Results HRVs were detected in 315 (16%) of 1919 hospitalized patients and 27 (9.6%) of 280 controls. Children had the highest frequency of HRV detections (hospitalized: <1 year: 29%, 1–4 year: 29%, ≥65 years: 9%; controls: <1 year: 24%, 1–4 year: 14%, ≥65 years: 2.8%). Enrollment adjusted hospitalized HRV detection rates were highest among persons aged <1 year (1038/100,000 persons/year), 1–4 years (457), and ≥65 years (71). All three HRV species were identified, HRV-A was the most common species in most age groups including children aged <1 year (61%) and all adult age groups. HRV-C was the most common species in the 1–4 year (51%) and 5–19 year age groups (54%). Compared to controls, hospitalized adults (≥19 years) and children were more likely to have HRV detections (odds ratio [OR]: 4.8, 95% confidence interval [CI]: 1.5, 15.8; OR: 2.0, CI: 1.2, 3.3, respectively) and hospitalized children were more likely to have HRV-A (OR 1.7, CI: 0.8, 3.5) or HVR-C (OR 2.7, CI: 1.2, 5.9) detection. Conclusions HRV rates were high among hospitalized children and the elderly but asymptomatic children also had substantial HRV detection. HRV (all species), and HRV-A and HRV-C detections were epidemiologically-associated with hospitalized illness. Treatment or prevention modalities effective against HRV could reduce hospitalizations due to HRV in Thailand.

Epidemiology of Severe Pneumonia Caused by Legionella longbeachae, Mycoplasma pneumoniae, and Chlamydia pneumoniae: 1-Year, Population-Based Surveillance for Severe Pneumonia in Thailand

BACKGROUND Legionella species, Mycoplasma pneumoniae, and Chlamydia pneumoniae are recognized as important causes of pneumonia in high-income countries, but their significance in middle-income countries, such as Thailand, is unknown. METHODS Population-based surveillance identified inpatient 3489 cases of clinically-defined pneumonia in a rural Thai province for 1 year. Patients who had a chest radiograph performed (for 2059 cases of pneumonia) were enrolled in an etiology study (which included 755 cases of pneumonia among 738 patients). Paired serum, nasopharyngeal swab, and urine specimens were obtained for diagnostic immunologic and molecular tests. Patients aged <18 years were not systematically tested for Legionella species. We report a lower limit of incidence (observed incidence) and an upper limit extrapolated to persons not tested or not enrolled in the study. RESULTS The incidence of pneumonia due to Legionella longbeachae requiring hospitalization was 5-29 cases per 100,000 population. No case of Legionella pneumophila pneumonia was observed. The definite C. pneumoniae pneumonia incidence was 3-23 cases per 100,000 population; rates were highest among patients aged <1 year (18-166 cases per 100,000 population) and those aged >or=70 years (23-201 cases per 100,000 population). M. pneumoniae pneumonia had a similar age distribution, with an overall incidence of 6-44 cases per 100,000 population. These pathogens were associated with 15% of all cases of pneumonia. A nonsignificantly higher proportion of patients with pneumonia associated with L. longbeachae, compared with patients with pneumonia associated with M. pneumoniae or C. pneumoniae, required supplemental oxygen or mechanical ventilation (45% vs. 18%; P<.1). Among patients with atypical pneumonia, only 15% received antibiotics with activity against the associated pathogen. CONCLUSION M. pneumoniae, C. pneumoniae, and L. longbeachae, but not L. pneumophila, are frequently associated with severe pneumonia in rural Thailand. Few patients receive antibiotics that cover atypical pathogens.

Antibiotic Use in Thailand: Quantifying Impact on Blood Culture Yield and Estimates of Pneumococcal Bacteremia Incidence

No studies have quantified the impact of pre-culture antibiotic use on the recovery of individual blood-borne pathogens or on population-level incidence estimates for Streptococcus pneumoniae. We conducted bloodstream infection surveillance in Thailand during November 2005–June 2008. Pre-culture antibiotic use was assessed by reported use and by serum antimicrobial activity. Of 35,639 patient blood cultures, 27% had reported pre-culture antibiotic use and 24% (of 24,538 tested) had serum antimicrobial activity. Pathogen isolation was half as common in patients with versus without antibiotic use; S. pneumoniae isolation was 4- to 9-fold less common (0.09% versus 0.37% by reported antibiotic use; 0.05% versus 0.45% by serum antimicrobial activity, P < 0.01). Pre-culture antibiotic use by serum antimicrobial activity reduced pneumococcal bacteremia incidence by 32% overall and 39% in children < 5 years of age. Our findings highlight the limitations of culture-based detection methods to estimate invasive pneumococcal disease incidence in settings where pre-culture antibiotic use is common.

High Prevalence of Cryptococcal Infection Among HIV-Infected Patients Hospitalized With Pneumonia in Thailand

Cryptococcal antigenemia was common among human immunodeficiency virus-infected patients hospitalized with acute respiratory illness in Thailand. Few clinical differences were evident between antigenemic and nonantigenemic HIV-infected patients. Cryptococcal infection was a possible etiologic agent of pulmonary disease in many antigenemic patients.

Serotypes and antimicrobial resistance of streptococcus pneumoniae in Thailand 2002-2004.

Information on pneumococcal isolates is limited in Asia. Among children younger than 5 years in rural Thailand, nasopharyngeal colonization was 60%, and 55% of carried and 62% of invasive isolates were serotypes in the 7-valent pneumococcal conjugate vaccine. Nonsusceptibility was common among the serotypes included in the vaccine. Pneumococcal conjugate vaccine might be a useful prevention tool in Thailand.

Hospitalizations for Acute Lower Respiratory Tract Infection Due to Respiratory Syncytial Virus in Thailand, 2008–2011

BACKGROUND Few population-based estimates of the incidence of respiratory syncytial virus (RSV) infection in low- or middle-income countries are available. We describe the incidence and epidemiology of hospitalizations for RSV-associated acute lower respiratory tract infection (ALRI) detected by active population-based surveillance in 2 rural Thailand provinces during 2008-2011. METHODS Patients hospitalized with ALRI were systematically sampled. Consenting patients provided nasopharyngeal swab specimens for RSV testing by real-time reverse-transcription polymerase chain reaction. RESULTS Of 13 982 enrolled patients hospitalized with ALRI, 1137 (8.1%) were RSV positive. After adjustment for sampling and nonenrollment, the incidence of RSV-associated ALRI hospitalization was 85 cases per 100,000 persons/year. The highest rates occurred among children aged <5 years (981 cases per 100,000 persons/year) and <1 year (1543 cases per 100,000 persons/year). Rates were low among older children and young adults but high among persons aged >65 years (130 cases per 100,000 persons/year). Eight (0.7%) RSV-infected study patients died during hospitalization. Annual RSV hospitalizations peaked during July-October with almost no documented RSV hospitalizations during January-June. CONCLUSIONS Our findings demonstrate the substantial contribution of RSV to global ALRI burden, especially in children aged <5 years and the elderly, and underscore the urgent need for effective prevention measures.

Incidence and Epidemiology of Hospitalized Influenza Cases in Rural Thailand during the Influenza A (H1N1)pdm09 Pandemic, 2009–2010

Background Data on the burden of the 2009 influenza pandemic in Asia are limited. Influenza A(H1N1)pdm09 was first reported in Thailand in May 2009. We assessed incidence and epidemiology of influenza-associated hospitalizations during 2009–2010. Methods We conducted active, population-based surveillance for hospitalized cases of acute lower respiratory infection (ALRI) in all 20 hospitals in two rural provinces. ALRI patients were sampled 1∶2 for participation in an etiology study in which nasopharyngeal swabs were collected for influenza virus testing by PCR. Results Of 7,207 patients tested, 902 (12.5%) were influenza-positive, including 190 (7.8%) of 2,436 children aged <5 years; 86% were influenza A virus (46% A(H1N1)pdm09, 30% H3N2, 6.5% H1N1, 3.5% not subtyped) and 13% were influenza B virus. Cases of influenza A(H1N1)pdm09 first peaked in August 2009 when 17% of tested patients were positive. Subsequent peaks during 2009 and 2010 represented a mix of influenza A(H1N1)pdm09, H3N2, and influenza B viruses. The estimated annual incidence of hospitalized influenza cases was 136 per 100,000, highest in ages <5 years (477 per 100,000) and >75 years (407 per 100,000). The incidence of influenza A(H1N1)pdm09 was 62 per 100,000 (214 per 100,000 in children <5 years). Eleven influenza-infected patients required mechanical ventilation, and four patients died, all adults with influenza A(H1N1)pdm09 (1) or H3N2 (3). Conclusions Influenza-associated hospitalization rates in Thailand during 2009–10 were substantial and exceeded rates described in western countries. Influenza A(H1N1)pdm09 predominated, but H3N2 also caused notable morbidity. Expanded influenza vaccination coverage could have considerable public health impact, especially in young children.

Incidence of Bacteremic Melioidosis in Eastern and Northeastern Thailand

Burkholderia pseudomallei, the causative agent of melioidosis, is endemic in northeastern Thailand. Population-based disease burden estimates are lacking and limited data on melioidosis exist from other regions of the country. Using active, population-based surveillance, we measured the incidence of bacteremic melioidosis in the provinces of Sa Kaeo (eastern Thailand) and Nakhon Phanom (northeastern Thailand) during 2006-2008. The average annual incidence in Sa Kaeo and Nakhon Phanom per 100,000 persons was 4.9 (95% confidence interval [CI] = 3.9-6.1) and 14.9 (95% CI = 13.3-16.6). The respective population mortality rates were 1.9 (95% CI = 1.3-2.8) and 4.4 (95% CI = 3.6-5.3) per 100,000. The case-fatality proportion was 36% among those with known outcome. Our findings document a high incidence and case fatality proportion of bacteremic melioidosis in Thailand, including a region not traditionally considered highly endemic, and have potential implications for clinical management and health policy.

Hospitalization due to human parainfluenza virus–associated lower respiratory tract illness in rural Thailand

Background  Human parainfluenza viruses (HPIVs) are an important cause of acute respiratory illness in young children but little is known about their epidemiology in the tropics.