Males, ages ≥ 45 years, businessperson, floating population, and rural residents may be considered high-risk groups for tuberculosis infection in Guangzhou, China: a review of 136,394 tb confirmed cases.

June 19, 2013

To the editor

Tuberculosis (TB) is a disease caused by the chronic and continuous infection of the pathogen Mycobacterium tuberculosis (M. tuberculosis) 4. It is a major public health problem that has threatened the health of human beings worldwide, especially in developing countries. Although the World Health Organization (WHO) has launched the “Global Plan to Stop Tuberculosis”, which aims to save a million lives by 201511, China, the second among the 22 high-burden countries, has different incidences and prevalence of TB in different provinces. As the largest trading city in southern China, Guangzhou, located in the southern subtropical, with over 7.94 million registered inhabitants and 4.76 million floating population6, here TB has become one of the extremely common airborne transmission diseases. According to the document from Guangzhou Center for Disease Control and prevention (GZCDC), a total of 19,701 cases were newly diagnosed in 2012, yielding annual incidence rate of 1545.01 per 100,000 inhabitants, public health authorities are concerned about its unacceptably high prevalence.

In this study, we obtained data of TB cases in Guangzhou during the period of 2007-2012, from the National Notifiable Disease Report System (NNDRS). Descriptive statistics are used to describe the basic features of TB confirmed cases, chi-square test was used to exam linear trends in proportions by years. In China, TB is a notifiable Class-B communicable disease, all cases were diagnosed according to the unified diagnostic criteria issued by Chinese Ministry of Health, for a patient's illness to meet the case definition for TB the clinical signs (cough, coughing up blood, night sweat, fatigue, fever, and weight loss, etc) must be present and taken samples for laboratory confirmation (TB skin test, TB blood test, sputum smears and cultures, chest radiograph (X-ray), and appropriate laboratory tests). A standard form was adopted by local physicians and epidemiologist to collect individual information on each TB case, including age, address, onset date, diagnosis, and laboratory test result. Routine case reporting is done by hospitals through NNDRS within 24 hours.

From January 1, 2007 to December 31, 2012, a total of 136,394 TB confirmed cases were reported in Guangzhou, of which 69.83% (95,240) were male patients and 30.17% (41,154) were female patients. Annual incidence rate from 2007 to 2012 was 2612.33, 2384.31, 2103.75, 1822.62, 1609.18, and 1545.01 (per 100,000), respectively, showing a declining trend. The age ranged from 0.6 to 103 years (mean age was 40.41 years). The proportion of confirmed cases between <5, 6-19, 20-44, 45-64, and >65 was 0.43% (581), 6.63% (9038), 2.61% (3565), 78.33% (106842), and 12.00% (16368), respectively. By occupation, the highest proportion of cases was businessperson, which accounted for 29.31% (39,974) of all cases, followed by workers and farmers, which accounted for 23.01% (31,380) and 14.70% (20,050), respectively. Majority of cases lived in rural areas (69.65%). Notably, from 2007 to 2012, the proportion of patients identified as the floating population was 21.47% (5591), 19.29% (4843), 22.43% (5264), 28.06% (6070), 31.82% (6507), and 33.41% (6583), , p = 0.00 (Table 1).

Table 1

Statistical summary of tuberculosis cases reported in Guangzhou, China, 2007-2012

	2007		2008		2009		2010		2011		2012		2007-2012
	N	%	N	%	N	%	N	%	N	%	N	%	N	%
Gender
Female	7701	29.58	7482	29.80	7083	30.19	6681	30.88	6236	30.49	5971	30.31	41154	30.17
Male	18335	70.42	17625	70.20	16381	69.81	14953	69.12	14216	69.51	13730	69.69	95240	69.83
Age
0-5	104	0.40	88	0.35	112	0.48	104	0.48	85	0.42	88	0.45	581	0.43
6-19	1781	6.84	1770	7.05	1635	6.97	1421	6.57	1299	6.35	1132	5.75	9038	6.63
20-44	699	2.68	684	2.72	609	2.60	612	2.83	536	2.62	425	2.16	3565	2.61
45-65	20257	77.80	19208	76.50	18239	77.73	16885	78.05	16360	79.99	15893	80.67	106842	78.33
>65	3195	12.27	3357	13.37	2869	12.23	2612	12.07	2172	10.62	2163	10.98	16368	12.00
Patient type
Local residents	20445	78.53	20264	80.71	18200	77.57	15564	71.94	13945	68.18	13118	66.59	101536	74.44
Floating people	5591	21.47	4843	19.29	5264	22.43	6070	28.06	6507	31.82	6583	33.41	34858	25.56
Occupation
Business	7131	27.39	6532	26.02	6679	28.46	5988	27.68	6830	33.40	6814	34.59	39974	29.31
Worker	7034	27.02	6932	27.61	5921	25.23	5753	26.59	3384	16.55	2356	11.96	31380	23.01
Farmer	4116	15.81	3914	15.59	3355	14.30	2850	13.17	3054	14.93	2761	14.01	20050	14.70
Household	2689	10.33	2543	10.13	2851	12.15	2638	12.19	3347	16.37	3930	19.95	17998	13.20
Retirees	2979	11.44	3249	12.94	2825	12.04	2837	13.11	2564	12.54	2703	13.72	17157	12.58
Student	1049	4.03	964	3.84	956	4.07	849	3.92	741	3.62	638	3.24	5197	3.81
Clerk	591	2.27	541	2.15	448	1.91	338	1.56	226	1.11	206	1.05	2350	1.72
Teacher	201	0.77	172	0.69	165	0.70	135	0.62	104	0.51	81	0.41	858	0.63
Scattered children	88	0.34	92	0.37	115	0.49	114	0.53	94	0.46	94	0.48	597	0.44
Doctor	79	0.30	109	0.43	109	0.46	82	0.38	66	0.32	74	0.38	519	0.38
Driver	22	0.08	22	0.09	15	0.06	13	0.06	7	0.03	11	0.06	90	0.07
Fisherman	15	0.06	12	0.05	11	0.05	15	0.07	17	0.08	15	0.08	85	0.06
Kindergarten children	25	0.10	10	0.04	7	0.03	8	0.04	2	0.01	6	0.03	58	0.04
Herdsman	8	0.03	6	0.02	4	0.02	5	0.02	8	0.04	9	0.05	40	0.03
Nurse	9	0.03	9	0.04	3	0.01	9	0.04	8	0.04	3	0.02	41	0.03
Residence
City/town	8478	32.56	7932	31.59	7098	30.25	6431	29.73	5879	28.75	5578	28.31	41396	30.35
Rural	17558	67.44	17175	68.41	16366	69.75	15203	70.27	14573	71.25	14123	71.69	94998	69.65

Despite the overall incidence rate of TB declined gradually in recent years, we found the proportion of patients identified as the floating population appeared an increasing trend by years. Similar observation was also reported in Wuhan city of China15. In Guangzhou, majority of the floating population are rural-to-urban migrants, they usually lived in crowded places, with poor sanitation, low health risk awareness, and limited access to health care10 13. Numerous studies revealed that compared to permanent residents, the floating population have higher incidence in many infectious diseases such as malaria1, measles5, and influenza7, etc. Furthermore, it is also reported that the floating population are at greater risk for HIV infection than the general Chinese population14. Once people coinfected with TB and HIV, the risk of reactivation increases to 10% per year12, mortality increases dramatically9. This suggested that more efforts should be directed towards improvement of TB control among the floating population.

In contrast to the finding from Africa where TB primarily affects adolescents and young adults3, we found more than 90% of cases reported were in the ages ≥ 45 years. This is because since 1978, BCG vaccine has been incorporated into Child Immunization Program in China2. According to the routine immunization schedule, BCG is given to children under 15 years of age, free of charge. However, most people at present aged 45 years and older have not been vaccinated, this make them more susceptible to TB infection compared to those vaccinated. We also found that the majority of TB cases are rural residents, this is consistent with the study from most of Chinese cities8. In addition, by occupation, businesspeople accounted for the highest proportion of cases, the gender of TB confirmed cases was more heavily male than female. One possible explanation for this might be that these people are more active in social activities, therefore more likely to contact with TB cases.

Taken together, we reported that the TB infection continued to have fairly high prevalence in Guangzhou, China. Among the patients, the floating population has made up a noticeable percentage and has appeared as an increasing trend on years. The male, age ≥ 45 years, businesspersons, and rural residents may be also considered high-risk groups for tuberculosis infection. This information may be useful for TB control programs in the future.