Seasonal Variation of Newly Notified Pulmonary Tuberculosis Cases from 2004 to 2013 in Wuhan, China

China. PLoS ONE 9(10): e108369. doi:10.1371/journal.pone.0108369 Seasonal Variation of Newly Notified Pulmonary Tuberculosis Cases from 2004 to 2013 in Wuhan, China Xiaobing Yang 0 Qionghong Duan 0 Jianjie Wang 0 Zhengbin Zhang 0 Gaofeng Jiang 0 Igor Mokrousov, St. Petersburg Pasteur Institute, Russian Federation 0 1 Department of Tuberculosis Control, Wuhan Tuberculosis Institution , Wuhan, Hubei , China , 2 Department of Infectious Diseases Prevention and Control, Wuhan Center for Disease Prevention and Control , Wuhan, Hubei , China , 3 School of Public Health, Medical College, Wuhan University of Science and Technology , Wuhan, Hubei , China Background: Although there was a report about the seasonal variation in Wuhan city, it only analyzed the prevalence data of pulmonary tuberculosis (TB) cases, and just studied the seasonality by subgroup of smear positive and negative from 2006 to 2010 by spectral analysis. In this study, we investigated the seasonality of the total newly notified pulmonary TB cases by subgroups such as time period, sex, age, occupation, district, and sputum smear result from 2004 to 2013 in Wuhan by a popular seasonal adjustment model (TRAMO-SEATS). Methods: Monthly pulmonary TB cases from 2004 to 2013 in Wuhan were analyzed by the TRAMO-SEATS seasonal adjustment program. Seasonal amplitude was calculated and compared within the subgroups. Results: From 2004 to 2013, there were 77.76 thousand newly notified pulmonary TB cases in Wuhan, China. There was a dominant peak spring peak (March) with seasonal amplitude of 56.81% and a second summer peak (September) of 43.40%, compared with the trough month (December). The spring seasonal amplitude in 2004-2008 was higher than that of 20092013(P,0.05). There were no statistical differences for spring seasonal amplitude within subgroups of gender, age, district, and sputum smear result (P.0.05). However, there were significant differences in spring seasonal amplitude by occupation, with amplitude ranging from 59.37% to 113.22% (P,0.05). The summer seasonal amplitude in 2004-2008 was higher than that of 2009-2013(P,0.05). There were no statistical differences in summer seasonal amplitude within subgroups of gender, district, sputum smear result(P.0.05). There were significant differences in summer seasonal amplitude by age, with amplitude ranging from 36.05% to 100.09% (P,0.05). Also, there were significant differences in summer seasonal amplitude by occupation, with amplitude ranging from 43.40% to 109.88% (P,0.05). Conclusions: There was an apparent seasonal variation in pulmonary TB cases in Wuhan. We speculated that spring peak in our study was most likely caused by the increased reactivation of the latent TB due to vitamin D deficiency and high PM2.5 concentration, while the summer peak was mainly resulted from the enhanced winter transmission due to indoor crowding in winter, overcrowding of public transportation over the period of the Spring Festival and health care seeking delay in winter. - " XY and QD are co-first authors on this work. Although China has achieved a great progress in TB control, tuberculosis is still a public health problem [1]. In 2012, it was estimated that there were approximately 1.0 million newly diagnosed cases, 1.4 million prevalent cases, and 44 thousand deaths that were due to TB in China [2]. In 1996, Douglas reported an unique seasonal pattern (summer peak) of tuberculosis compared with most other respiratory diseases [3]. Since then, there were many other researchers recognized various patterns of seasonality of TB [415], except for a few studies in which no obvious pattern of seasonality of TB was found [16]. Some studies showed that there was a single springearly summer peak [48], while other studies found a single summer peak [3,9,10]. Additionally, a few of other studies showed a dominant peak (spring/summer) along with a second peak (summer/winter) [11,12]. What caused the difference? Researchers linked the seasonal variation of TB to two kinds of factors. Firstly, factors like indoor crowding in winter could lead to an increase of TB transmission (extrinsic infection). Secondly, vitamin D deficiency and high epidemic of other respiratory diseases could cause impaired immunity which would result in TB reactivation (intrinsic reactivation). However, questions arise. Which factor is the dominant reason for seasonality of TB? Are these the only influencing factors in term of extrinsic infection or intrinsic reactivation of TB? To examine those issues, we studied the seasonality of TB in Wuhan, China. Wuhan city with 10 million residents is the fourth largest city in China, and also one of the most important transportation junctions for the whole country. There are only a few studies reporting the seasonal variation of TB in China till now. The first one was conducted in Hong Kong from 1991 to 2002 [10], the second one was about the whole country from 2004 to 2012 [15], and the third study explored the seasonality of pulmonary TB in Wuhan from 2006 to 2010 [12]. But the above report in Wuhan mentioned prevalence data of pulmonary TB cases, and studied the seasonality only by subgroup of smear positive and negative. In this study, we used newly notified pulmonary TB data, and investigated the seasonality of total pulmonary TB cases and by subgroups such as time period, sex, age, occupation, district, and sputum smear result from 2004 to 2013 in Wuhan. Although there are a lot of mathematic models used to analyze the seasonality, TRAMO-SEATS (Time Series Regression with ARIMA Noise, Missing Observations and Outliers, TRAMOSEATS) applied in our study is one of the most popular seasonal adjustment time series models over the world. Our study explored the seasonal variation of pulmonary TB in Wuhan, aimed to give the clue to reveal the characteristics of TB epidemic and the influencing factors and to develop suitable TB control measurements. Materials and Methods Data The Data of confirmed pulmonary TB cases (laboratory or clinical verified) by month in Wuhan city, Hubei Province, China from Jan 2004 to Dec 2013 was obtained from the internet-based National Infectious Diseases Reporting System(NIDRS), Chinese Center for Disease Control and Prevention. It is mandatory for all hospitals, clinics, disease prevention and control institutions and other designated health care establishments to report all newly diagnosed pulmonary TB cases timely and directly via NIDRS. From NIDRS, we also obtained the data of sex, age, occupation, district, and sputum smear result of pulmonary TB cases. Seasonal Adjustment of Time Series Monthly pulmonary TB case counts were analyzed by the TRAMO-SEATS seasonal adjustment program which is an advanced seasonal adjustment program paralleled with X-12ARIMA program [17]. It is a very stable and efficient model developed by the bank of Spain. In the TRAMO-SEATS program, the original time series is decomposed into three basic components (...truncated)