Epidemiologic changes of infectious diseases in the post-SARS era in China, 2004–2018

Epidemiological changes

Although the overall incidence of infectious diseases in China showed an increasing trend from 2004 to 2018, fortunately, the trend levelled off after 2010. Overall mortality from infectious diseases has risen significantly, with HIV/AIDS replacing tuberculosis and rabies as the leading cause of death from infectious diseases since 2008. The incidence of most vaccine-preventable diseases remained low, but seasonal changes in seasonal influenza, mumps, pertussis, and rubella suggested that these diseases, especially pertussis and seasonal influenza (incidence increased rapidly over the 15 years), should remain a public health priority. Among quarantinable diseases, classic infectious diseases such as cholera and plague almost disappeared. Except dengue and scarlet fever, the incidence of vector-borne diseases and bacterial infections diseases showed a decreasing trend. Over the 15 years, dengue and scarlet fever cases increased 20.7-fold and 4.2-fold, respectively. It is worth noting that, through regional and inter-departmental cooperation, such as the Five Middle Provinces and Three Southern Provinces Malaria Joint Control and Prevention Programme, and the improvement of the reference laboratory system for malaria diagnosis, and the implementation of the ‘1–3-7’ malaria surveillance and response strategy, China was certified by WHO in 2021 as the 40th malaria free country. However, continued increase in imported cases is a current challenge [7,8,9]. In contrast to the sharp decline in indigenous cases, imported malaria cases showed an explosive growth, with the percentage rising from 16.2% in 2004 to 99.9% in 2017 [10]. It is also worth noting that, due to the widespread distribution of Anopheles sinensis in China, the possibility of malaria comeback still exists, especially P. vivax malaria. Therefore, China still needs to remain vigilant against the resurgence of malaria. It is necessary to maintain a surveillance and response system and focus on hot spots and risk groups, with timely detection of imported cases, rapid reporting, and prevention of continued transmission. In addition, epidemiological and entomological surveillance is also necessary [10]. Increased incidences of hepatitis C, syphilis, and in particular HIV/AIDS, suggested that sexually transmitted diseases became an important new focus. Other gastrointestinal or enterovirus borne diseases still had relatively high prevalence despite continuous declines in dysentery and typhoid/paratyphoid. A clear geographic distribution of infectious diseases was observed, with bacterial infections and zoonotic diseases occurring more frequently and carrying a disproportionate health burden in western China.

Morbidity of Hepatitis B and mumps were dominant in vaccine-preventable diseases. Although the incidence of hepatitis B has declined since 2007, it remained one of the highest incidence infectious diseases in China for 15 years. With the implementation of the national immunization program and the improvement of sanitary conditions, the incidence of hepatitis A and B in Chinese adolescents and children has decreased significantly, while that in Chinese adults has increased [11, 12]. Thanks to the expanded immunization program, the incidence of mumps began to decline in 2012, but has increased since 2015, and it is now the most common infection among children aged 3–10 years [13]. Notably, diseases such as pertussis and seasonal influenza have experienced unexplained resurgence worldwide over the past decade, raising concerns about vaccine effectiveness, coverage, and more [14].

Tuberculosis is one of the top ten causes of death globally, with its death toll second only to HIV/AIDS in China. From 2004 to 2018, the tuberculosis incidence ranking dropped from 1st to 4th, with a significant decrease from 74.64 to 59.27 cases per 100, 000 (APC = -3.1%, P < 0.001). The national tuberculosis control programme, which began in 1991, was likely to be the primary cause of the decline [15]. At present, drug-resistant tuberculosis is a major threat to the control and elimination of tuberculosis in China [16]. In 2017, approximately 14% of tuberculosis patients worldwide died from MDR-TB [17].

Incidence of scarlet fever has been increasing globally. Outbreaks have occurred in Vietnam [18], Hong Kong [19], and the United Kingdom one after another since 2008 [20]. The relaxation of family planning policies and the increasing susceptible population have led to the resurgence of scarlet fever [21, 22]. This prompted public health departments to establish school-based surveillance and emergency response systems. Similar measures can help combat hand-foot-mouth disease, infectious diarrhea and other susceptible childhood diseases, but their effectiveness was unclear [23]. Scarlet fever was predominant among children aged 1 to 9 years in western and northern China, while tuberculosis was the main disease among people aged 0 and older than 9 years in southern China. The regional heterogeneity of morbidity indicated that different regions should carry out the prevention and control of infectious diseases according to their own epidemiological characteristics.

During the studied period, HIV/AIDS incidence and deaths in China continued to increase, especially in males, and the infection in younger population showed an upward trend [11]. High-risk sexual behavior appeared to be one of the reasons for the increasing incidence of HIV/AIDS [24]. As of the end of September 2018, 850,000 people living with HIV infection and 262,000 deaths were reported, and sexual behavior was the main route of transmission. In 2017, heterosexual transmission accounted for 69.6% of reported infections, and male homosexual transmission accounted for 25.5% [25]. Insufficient sex education, pursuit of casual sex, and social media hype seemed to be the factors contributing to the increasing incidence. Although the government has launched response policies, a series of measures are urgently needed for policy implementation, including publicity campaigns and more attention from the education sector, family and school-based sex education, and purification of the network environment [24].

Benefited from public health interventions and mass vaccination programmes, the overall morbidity and mortality from infectious diseases in China have declined sharply in recent decades. However, after the SARS outbreak in 2003, the overall incidence in China showed a gradual upward trend, which we confirmed in our study of 44 major infectious diseases [1]. Fortunately, this trend changed after 2010. Several factors may explain this growing trend. First, the timeliness of reporting has been improved. Many emerging infectious diseases have abrupt onset, high fatality rate, difficult early detection and diagnosis, and lack of targeted prevention and control measures. Thanks to the improvement of the monitoring system and the medical diagnosis, more occult cases have been discovered. In addition, the development of health care, such as the widespread use of polymerase chain reaction (PCR), has made the diagnosis of diseases more convenient. In fact, we often see a significant increase in the diagnosis of a disease when some fast, convenient and highly specific techniques are developed and used in medical applications [26]. Second, large-scale population movement increases the difficulty of prevention and control, and measures such as vaccination are difficult to implement. Frequent international business exchanges increase the risk of cross-border transmission of infectious diseases and unsafe sex increases the risk of sexually transmitted diseases. Third, the environment and the existing production and lifestyle promote the spread of infectious diseases. The urban and rural environmental sanitation in some areas is in a worrying situation, and the traditional production and lifestyle make zoonotic diseases continue to occur. Overall, current prevention and control work in China is facing dual pressures from traditional and emerging infectious diseases. Prominent problems include backward infrastructure, weak monitoring and testing capabilities, insufficient funding, and serious shortage of professionals. Implementation of relevant provisions of the Law on the Prevention and Control of Infectious Diseases should be further strengthened in order to build strong foundations and make up for shortcomings. More attention should be paid to talent team building and professional capabilities improvement, along with the increasing investment in hardware such as equipment and facilities.

Recommendation for health promotion

Over the past few decades, China has adopted targeted strategies to prevent the spread of infectious diseases. Some measures have been proven to be effective and can provide insights and important lessons for other developing countries. First of all, improving the system of laws, regulations and policies. Legalize, institutionalize, standardize and standardize diseases prevention and control work. Secondly, it is vital to build a tight public health monitoring network. The national disease control information system of the national health security information project has been put into operation, and the world’s largest, horizontal and vertical disease and health risk factor monitoring network has been built, and the monitoring network of key endemic diseases and drinking water quality covers all townships and towns in China, and the monitoring and intervention system of common diseases and health hazards of students who are mainly regarded as the nearest is becoming more and more perfect. For example, improved sanitation and water supply facilities, improved blood collection safety and large-scale vector control can add to the successful prevention of infectious diseases.

Strength and limitation

Some limitations of our study should be noted. First, the effectiveness of monitoring systems and the accuracy of diagnosis based on data from reporting systems may be overestimated. Second, incidence may be underestimated due to self-selection bias, as people with a particular infectious disease are more likely to avoid screening than those without the infection. In addition, potential biases may affect morbidity and mortality reporting due to differences in the level of medical care in different regions, the level of hospital diagnosis, or inclusion/exclusion criteria.