Given the population size of China (1.3 billion persons) 
, the varied health utilization and economic development, the diverse climate (tropical to subarctic), and the range of population densities, the burden of pneumonia in China would be expected to be large and highly variable across regions. Despite overall trends from these studies suggesting that pneumonia incidence and mortality are stable or decreasing, pneumonia continues to be a major public health concern in China 
. The studies in this review found incidence of pneumonia in children <5 years of age that were as low as what has been estimated for the developed world globally (0.05 episodes per person-year) and that were as high as what has been estimated for the developing world (0.29 episodes per person-year) 
. The studies included in this review reported pneumonia incidence for children <5 years of age (0.06–0.27 episodes per person-year from 1985 to 2008) that was similar or less than what has been estimated for China (0.22 episodes per person-year in 2008) 
. Although the studies reported a wide range of pneumonia mortality estimates (184–1,223 deaths per 100,000 population), these are consistent with pneumonia remaining the leading cause of childhood mortality in China 
. While the data summarized here provide insights into pneumonia in China, they also serve as a reminder that reliable and high quality national and regional data on pneumonia incidence and etiology are needed to adequately direct prevention and control efforts.
Perhaps the largest limitation to this study is that study comparisons of morbidity and mortality rates were constrained by the wide variation and quality of the study designs. This is particularly evident in the wide range of mortality estimates among the different studies. In general, the incidence estimates were higher when the more standardized WHO case definition was used compared with estimates obtained from physician diagnosis; however, there was significant variability even among studies that used similar case definitions. The use of a standard pneumonia case definition that is designed for surveillance and epidemiologic research would improve generalizability and could allow for direct comparisons of incidence and mortality estimates in China and elsewhere 
. Most studies spanned multiple years, which would account for differences in seasonality of pneumonia, but a few were conducted for one year or less. Although a few of the studies reported large surveillance populations, many calculated incidence based on relatively small populations or did not report the population under surveillance. Most of these studies were conducted in large, urban centers primarily serving residents of densely-populated areas; few included adults or populations from rural western China. Although many of the studies were conducted prospectively, none calculated incidence using active, population-based surveillance and population denominators were not reliably measured in each study. Until standardized case definitions and appropriate surveillance methodology are applied, pneumonia incidence and mortality estimates should be interpreted cautiously.
In regions for which we identified published data, pneumonia incidence in China appears to be declining and mortality is stable or declining from the 1980s to the 2000s. There are several factors that could have contributed to these changes over time. China experienced substantial economic growth during these years, a trend that was more pronounced in the coastal (Eastern) areas. From the beginning of economic reforms in 1978 to 2006, China's gross domestic product (GDP) increased 5,719% from 362.4 billion RMB to 21,087.1 billion RMB 
. The income of the average Chinese person also improved during this time period; GDP per capita rose by 4,144% from 379 RMB to 16,084 RMB 
. Economic development may have led to improvements in healthcare quality and access to health services.
In addition to economic development, China is undergoing dramatic healthcare reform, including government-sponsored healthcare in rural areas 
. Declines in the incidence of pneumonia are likely attributable to the implementation of pneumonia intervention measures, such as technical training for village doctors, health education to parents, improved pneumonia surveillance and case management, and the use of vaccines against pneumonia in the routine immunization program (namely measles and pertussis). The improved detection and recognition of pneumonias following the SARS, avian influenza and 2009 influenza H1N1 epidemics could lead to more cases of pneumonia being promptly identified and treated. Large scale programs to introduce less polluting cookstoves in China have led to decreases in lung cancer and chronic obstructive pulmonary disease 
; studies from other countries suggest that reductions in exposure to indoor air pollution from solid fuels used for cooking can also lead to fewer cases of pneumonia 
. Other strategies, including better access to care, improved hygiene, and better nutrition may need strengthening to effectively reduce the incidence of pneumonia in China 
For many Chinese, adequate healthcare remains difficult to access; this review revealed a disparate incidence and mortality of pneumonia across different regions of China 
, some of which is likely due to inequalities in health care. For example, respirators and ventilators for children are not currently available in many county hospitals. Eastern China is more developed, whereas Western China is more rural. According to a report on national maternal and child health endorsed by the China Ministry of Health, UNICEF, and WHO, pneumonia is the leading cause of death in children under 5 years of age in some rural areas, and comprises a larger proportion of deaths in children under 5 years of age as the area becomes more rural 
. This report also demonstrated the decreasing trends in pneumonia mortality across China, especially in areas where few clinical studies have been completed.
Better access to proven public health interventions, including vaccines, is needed in the public sector in China. Vaccines against Haemophilus influenzae
type b (Hib), Streptococcus pneumoniae
, and influenza are not part of routine childhood vaccination programs in many countries worldwide 
; none of these vaccines are included in the routine childhood immunization schedule in mainland China. However, Hib and influenza vaccines are commonly available in many parts of China through vaccination clinics, and Hong Kong SAR is the first region in China, as well as Asia, where pneumococcal conjugate vaccine will be included in their routine childhood immunization program starting September 2009 
. In addition, Hong Kong SAR recommends seasonal influenza vaccine use in high risk groups. Vaccine clinical trials in other countries have estimated that 21% of radiologically confirmed pneumonia is caused by Hib 
and 36% by pneumococcus 
; over 10% of hospitalized pneumonia in children in nearby Thailand are due to influenza 
. Studies within China have suggested that Hib and pneumococcus are common causes of pneumonia in children 
, suggesting that widespread use of these two vaccines, as well as influenza vaccine, could reduce the incidence and mortality of pneumonia in China.
This paper has several strengths, particularly the inclusion of papers published in both the English and Chinese literature. A recent global review on childhood pneumonia incidence included only two of the 14 articles presented here, suggesting that articles not published in English are usually overlooked and difficult to obtain 
. We did not search three of the five major Chinese-language literature databases (the China National Knowledge Infrastructure China Academic Journals Full-text Database, Chinese Biomedical Literature Database, and Chinese Medical Current Content), so we may not have captured all relevant manuscripts; however, the two databases that we did search include some of the greatest number of journals and articles of the five major databases 
. In addition, this review includes information on all ages, although only two studies included adults. While global pneumonia prevention efforts often focus on children, the burden of pneumonia in adults and the elderly is also substantial. Importantly, interventions aimed at children may have underappreciated benefits on adults. For example, the introduction of universal childhood pneumococcal vaccination in the United States in 2000 resulted in significant declines in pneumococcal incidence in both children and adults. In 2003, the indirect effect of preventing invasive pneumococcal disease in adults was over twice the direct effect of preventing cases in children 
Comprehensive data on pneumonia incidence and mortality are essential for monitoring disease trends, guiding policy decisions, and prioritizing disease prevention and control strategies. For China, accurate information on the incidence and mortality of pneumonia, as well as data on cost, will be central for planning the addition of new vaccines to routine childhood immunization programs. Also, seasonal and pandemic influenza remain ever present global threats. Continued surveillance and consideration of influenza vaccination and other control measures are needed. In collaboration with the U.S. Centers for Disease Control and Prevention (CDC), China's CDC is implementing active, population-based surveillance for pneumonia in certain areas using a standard approach and case definitions. The surveillance system will aim to better define pneumonia incidence, identify etiologies, and guide important clinical and public health decisions. Increased laboratory capacity needs to be built to ensure continued rigorous surveillance and quick response to emerging threats. Together these improved surveillance and laboratory data should help improve detection, prevention and control of pneumonia throughout China.