Typhoid and paratyphoid are intestinal infections caused by the bacteria Salmonella
Typhi and Paratyphi and are transmitted by the fecal–oral route. Their main symptoms are digestive tract reaction. Infection may occur after consumption of food or water contaminated by feces or urine [1
]. The incubation period is mostly 3–42 days with an average of 14 days for typhoid fever and 2–15 days for paratyphoid. Their clinical manifestations are varied, including fever, fatigue, headaches, gastrointestinal reaction, and complications may develop in severe cases, such as intestinal bleeding and perforation [1
]. The World Health Organization (WHO) estimated that, globally, typhoid and paratyphoid patients in 2000 totaled 21.65 million, of whom 220,000 died [2
], and the number declined to 13.43 million in 2010 [3
]. The incidences of typhoid and paratyphoid in developed countries declined steadily by 0.13–1.2 per 100,000 as a result of a series of measures taken for water quality control and improved health facilities [4
]. Conditions favorable for these diseases are still common in Asia, Africa, and poor countries and thus have a great impact on social and economic development. China has always been among the high-incidence areas, with an incidence rate of about 10–50/100,000 before 1990, which dropped to 1.28/100,000 in 2009 [5
]. Zhejiang Province is economically developed, but historical incidences were higher there than the national average [5
]. Although the incidence rate in this province has fallen, typhoid and paratyphoid continue to be problematic intestinal diseases.
The geographical information system (GIS) is a widely used tool to explore the spatiotemporal characteristics of infectious diseases, which could help to monitor and prevent communicable diseases [9
]. Also, it makes it easy for researchers to identify the incidence difference of any infectious disease between regions via an incidence level map [10
In this paper, we aimed to investigate the epidemiological characteristics of typhoid and paratyphoid fevers and to detect high-risk populations and areas, thus providing a basis for the prevention and monitoring of typhoid and paratyphoid in Zhejiang Province.
In this study, we investigated the epidemiological trend of typhoid and paratyphoid fevers from 1953 to 2014, and further explored their temporal and spatial distribution, correlation between altitude and incidence, and characteristics regarding gender, occupation, and age.
The incidences of typhoid and paratyphoid fevers have fallen dramatically, and their fatality rate has declined since 1953, as reflected in the findings of a national investigation by Yan et al. [5
] and a local one in Deqing County by Xu [17
]. Intestinal infectious diseases in China have been significantly reduced since the implementation of the Patriotic Health Campaigns by the National Patriotic Health Committee and the health department in the 1970s and the introduction of the healthy policy of tubing water and toilet [18
]. The measures taken for tubing water and toilet have resulted in declining incidences of intestinal infectious diseases of various degrees in Jiaxing and Yuhuan [20
The Patriotic Health Campaign launched by the government at the beginning of the foundation of the People’s Republican of China helped reduce the incidence of all kinds of diseases and significantly improved public health [22
]. The incidence in 1969 fell to the lowest during the Cultural Revolution, which might be attributed to the fact that all the work in health epidemic prevention stations was stopped and case reports were incomplete. The same was true with Zhejiang Province. The outbreak of chloramphenicol-resistant M1 bacteria in 1988 led to the highest incidence in the history [23
]. In 2004, the China Information System for Diseases Control and Prevention was introduced and disease reporting became more convenient and reliable, which led to an abrupt increase in reporting and a false peak. Thanks to all the preventive measures taken for many years, the incidence was found to be 0.95 per 100,000 population in Zhejiang in 2014, indicating the province as a low-level area of typhoid and paratyphoid.
The plain areas are more greatly affected by heavy rains, typhoons, and floods than the mountainous and hilly areas in the summer and autumn, resulting in a higher probability of polluted water in low-altitude areas than in those of high altitude. Further, people in the plain drink river water, while those in the mountainous and hilly areas drink well water [24
]. These factors could explain the phenomenon that the incidences of typhoid and paratyphoid were lower in high-altitude areas than in the low-altitude plain in Zhejiang. Consistent with most studies [25
], the high incidence of disease gradually moved to the southeast coastal areas such as Taizhou, Wenzhou, and Ningbo from the north areas in Zhejiang around 1993. Zhoushan, Ningbo, and Taizhou were high-risk areas in the province, which was different from the previous results that Taizhou, Wenzhou, Jinhua, and Ningbo were the areas with high incidence of typhoid and paratyphoid in Zhejiang [28
]. The incidence of typhoid and paratyphoid in Ningbo has always been on the top of the list in Zhejiang since 1953, probably because the residents there have the habit of eating pickled raw or half-cooked seafood. The incidence in Zhoushan increased sharply to the highest in 1997 and by a large margin in 1998, possibly because of the continuous drought and lack of water. As an island, the disease prevention and control departments in Zhoushan pay much attention to drinking water disinfection and control the probable outbreak of typhoid and paratyphoid caused by water pollution after typhoons and storms [29
]. Similar to many other areas [30
], typhoid and paratyphoid could occur all year in Zhejiang, and the peak incidence often occurs in the summer and fall. The peak period every year was found to be in the months from April to October, which was different from the study by Zhou [33
], who reported that the peak period was from July to November when he analyzed the epidemiological characteristics of typhoid and paratyphoid in Xichang Municipality. The main reason for the high incidence in summer and autumn may be the influence of extreme weather such as typhoon in this period. The peak day of incidence in Zhejiang occurred in every month from March to September before 2006, after which the peak period fell around July 15. Some reasons could account for this phenomenon. The peak period was not stable until 2007. In principle, circular distribution is generally applicable to the disease that has only one peak period, which may explain the fluctuation of the peak day before 2007. This might be associated with the establishment of the China Information System for Diseases Control and Prevention, which makes timely case reporting possible so that information can be retrieved and analyzed immediately.
The majority of typhoid and paratyphoid cases were aged from 20 to 59 years. Zhejiang, due to rapid economic development, has a great number of migrant workers, and both aggregation and migration of the population could lead to the high incidence of typhoid and paratyphoid. The proportion of the patients over 60-years old increased yearly probably because of the weakening immunity of these people. Consistent with other intestinal infectious diseases [34
], the incidences of typhoid and paratyphoid were higher in men than in women. An explanation may be found in the fact that men might be engaged in more outdoor activities, had poorer hygiene habits, and ate more casually than women [36
]. When it comes to career, farmers, students, and workmen had higher incidences than others, which was close to other studies [32
]. The high percentage found for farmers may due to such factors as drinking water without disinfection or with incomplete disinfection, poor sanitation (outdoor latrines and widespread rubbish heaps), lack of health consciousness, and unhygienic diet.