This cross-sectional study was undertaken as part of the project “Investigation of nutrition and diet of patients with pulmonary tuberculosis in poor areas in China” supported by the World Health Organization Regional Office in the Western Pacific. It was conducted from November 2015 to April 2017 in two counties, Lingyun county in Guangxi province and Lin county in Shanxi Province. These two counties were national impoverished counties, and did good job in TB management. TB case notification rates in 2016 were 106.97 per 100,000 and 63.16 per 100,000 in Lingyun county and Lin county, respectively.
We focused our study on adult patients (age ≥ 18 years) with active TB who were registered in Tuberculosis management information system from Nov 1st, 2015 through May11th, 2017. Patients with extrapulmonary tuberculosis, and those aged 18 years and below or with severe complications were not eligible for the study. Pregnant or breast-feeding women, and those who declined to sign the consent form were also excluded.
As BMI is commonly used in nutrition assessment, we applied the prevalence of BMI < 18.5 which is also defined as malnutrition  in determining sample size. We assumed that the prevalence of malnutrition in the general population in poor areas and TB patients would be 6.7%  and 25.0% , respectively, and the required sample size was calculated to detect difference in the two proportions. The probability of a type I error was set at 0.05, the power of the study was estimated at 90% and the design effect was set at 1, determining a sample size of TB patients was 77 per study site. Considering participants’ refusal, we expanded the sample size to 150 per study site, and the final sample size of TB patients was 300 totally.
Socio-demographic and behavioral factors
Data for associated factors were taken from a questionnaire, including socio-demographic attributes (age, gender, education level, marital status, occupation and household income level) and behavioral variables (alcohol consumption, smoking status and eating out-of-home).
In line with Chinese Dietary Reference Intakes (DRIs) 2013 , we categorized patients’ ages into 3 groups: 18–49 years, 50–64 years, 65 years and above to facilitate comparisons. Educational level was classified into primary school and below, junior middle school and above. Household income level was proxied as annual household income and was grouped into < ¥20,000, ¥20,000 - ¥40,000, and ≥ ¥40,000 . Alcohol consumption was surveyed as drinking wine, beer and Chinese spirit now or ever. A smoker was defined as smoking now or smoking previously but have stopped smoking in the evaluation period. Eating out-of-home was defined as eating at least one meal away from one’s own home or their residents’ home during the survey . Severity of TB was grouped into two categories based on chest x-ray. Specifically, if the lesion was confined to two lung fields then it was defined as mild. If the lesion covered more than two lung fields or there were cavities, it was defined as severe .
Assessment of nutrient intake
Trained staffs performed face-to-face interviews for each participant to obtain dietary intake data through a 2-day 24-h dietary recall (24hdr) questionnaire, which was adapted from the method of 3-day 24hdr . Participants were instructed to record all food intake at home and away from home in the previous 2 days (one weekday and one weekend day). Consumptions of condiments were also recorded through a questionnaire. All questionnaires were completed after the patient registering in Tuberculosis management information system and before anti-tuberculosis treatment.
Total energy, four macronutrients and sixteen micronutrients were evaluated. Nutrient intakes of each patient were converted to calories, weight of protein and weight of micronutrients based on Chinese Food Composition Tables (CFCT) 2004 .
To evaluate whether the patients’ nutrients were sufficient, we compared mean daily nutrient intakes of TB patients to Recommended Nutrient Intakes (RNIs) and Adequate Intakes (AIs) by Chinese dietary reference intakes (DRIs) 2013. Recommended Nutrient Intakes is an estimate of the amount of a nutrient that meets the requirements of most people (97–98%) within a specific physiological group (sex, age, body size, physical activity, type of diet). Adequate Intakes means a recommended intake value based on observed or experimentally determined approximations or estimates of nutrient intake by a group (or groups) of healthy people .
Data of daily nutrient intakes were presented as means ± standard deviation (SD). As dietary recommendations are different for men and women, we compared TB patients’ daily nutrient intakes with DRIs by gender. Since protein-calorie malnutrition (PCM) is the most common form of undernutrition in TB patients, we only examined factors related to insufficient energy and protein intakes. Univariate logistic regression analysis was used to identify potential risk factors associated with inadequate energy and protein intakes in 300 TB patients. Age, gender, county and severity of TB were considered to be possible confounders in the multiple logistic regression model with stepwise selection. Patients were classified into two groups: below RNI/AI and above RNI/AI. A P-value of less than 0.05 was considered statistically significant. All analyses were performed using SAS 9.4 (SAS Institute Inc., Cary, NC, USA).
The study was carried out on the basis of China Health and Nutrition Survey (CHNS) 2015, from which the investigating method and tool were used in our study. All on-site investigations were carried out by the county-level CDC and interviewers were trained with a standard protocol. Data was checked for completeness and accuracy on the day of investigation and sampled by provincial CDC for verification later. All data was double-entered into a database specially designed for this project.