Based on 196 S. pneumoniae isolates collected during 4.4 years of bloodstream infection surveillance in 2 rural provinces, we estimated the overall incidence of hospitalization for pneumococcal bacteremia in rural Thailand at 3.5 per 100,000 person-years. Rates were highest among children <5 years old (11.1 per 100,000 person-years) and adults 65 years and older (13.6 per 100,000 person-years).
These findings demonstrate that S. pneumoniae
is an important cause of severe disease requiring hospitalization in Thailand. However, these data certainly underestimate the true incidence of pneumococcal bacteremia. First, we only captured hospitalized cases, and data from the United States suggest that most pneumococcal bacteremia cases in young children occur among outpatients 
. Second, despite increased use of blood cultures since implementation of automated blood culture processing in 2005, many patients who would likely have blood culture performed in higher resource settings do not receive them in rural Thailand. From May 2005 through June 2007, only 66% of patients with indications for blood culture had a culture performed and for patients <5 years old the proportion was just 47% 
. Furthermore, pre-culture antibiotic use remains common in this setting. We recently examined this issue and estimated that pre-culture antibiotics reduced our pneumococcal bacteremia incidence rates by 32% overall and 39% in children <5 years of age 
. Finally, our surveillance does not include other manifestations of invasive pneumococcal disease, such as meningitis, arthritis or osteomyelitis.
These incidence estimates are comparable to our previously reported estimates examining 72 S. pneumoniae
isolates from 23,853 blood cultures performed from May 2005 through June 2007 
. However, our previous report included estimates based on a combination of cases identified via S. pneumoniae
isolation and cases identified only by Binax NOW® immunochromatographic test (ICT) on broth of blood cultures that had a positive signal in the BactT/ALERT® machine but were negative on sub-culture (alarm positive, sub-culture negative). The current report does not include these ICT-only cases, because more recent investigations indicate false-positive tests can occur 
and we are formally evaluating this unlicensed application of ICT. Alarm positive, sub-culture negative bottles continue to pose a dilemma in our laboratories; from January through March 2010, 89 (2.2%) of 3891 blood cultures were alarm positive, sub-culture negative.
The proportion of fatal cases in Nakhon Phanom province (12%) was comparable to that reported in other publications from Thailand: 8.2% from Siripongpreeda et. al. (all invasive pneumococcal disease), 16% from Netsawang et. al (non-meningitis), 13.3% (non-meningitis) in Suwanpakdee et al
. By comparison, the case fatality rate in Sa Kaeo province (37%) seemed unusually high. Unfortunately, data detailing clinical characteristics, treatment, and underlying conditions were not available to investigate this unusually high case fatality rate. However, our data do suggest that severity of illness differed between the 2 provinces, with substantially more patients in Sa Kaeo requiring oxygen and intubation.
We documented consistent, statistically significant seasonal increases in pneumococcal bacteremia from December through March, which substantiates the seasonal increase noted in other reports from Thailand 
. This seasonal pattern coincides, approximately, with Thailand’s cool season (November through February) and the seasonal increases in pneumococcal disease observed in the U.S. and other temperate regions during the winter months 
. Interestingly, the pneumococcal bacteremia peaks in Thailand occurred during opposite times of year as Thailand’s usual influenza season 
, which differs from temperate climates where invasive pneumococcal disease and influenza peaks coincide 
. This report includes data during the 2009 influenza pandemic, which first peaked in Thailand from July to September 2009, during which time pneumococcal bacteremia rates were low ().
We observed that a high proportion of pneumococcal bacteremia cases among children aged <5 years were caused by serotypes covered by PCV10, and that with the addition of PCV13 serotypes, coverage increases from 74% to 92% for children <5 years old and from 61% to 82% overall. In a 2010 report, Thai researchers in the Bangkok area found that a similarly high proportion of IPD cases among children aged <5 years were caused by vaccine serotypes: 70% and 81% for PCV7 and 13 respectively 
. The Thailand National Institute of Health reported even higher proportions of vaccine serotypes among children aged <5 years with invasive disease (80% for PCV10 and 92% for PCV13) 
. Taken together these findings provide strong evidence that high coverage could be expected from PCV13 in Thailand.
All pneumococcal isolates were sensitive to penicillin, although we observed high rates of antibiotic non-susceptibility to a variety of other drugs, which is in agreement with many reports from Thailand 
and the region 
. Our finding that antibiotic non-susceptibility is significantly higher among PCV serotypes corroborates other reports from Thailand and suggests that enactment of PCV implementation could help reduce antibiotic non-susceptibility, as was seen in the U.S. after vaccine introduction 
These findings document the ongoing burden of hospitalized pneumococcal bacteremia, which represents a small fraction of the total pneumococcal disease burden. In previous work among adults, we found that blood culture alone underestimates the incidence of hospitalized pneumococcal pneumonia cases by at least 9-fold 
. Taken together with recent reports from other pneumococcal researchers in Thailand, our findings highlight the potential impact of PCV in Thailand and underscore the need for cost effectiveness data to inform vaccine policy discussions and decision making.