A cross-sectional study was conducted from January 2014 to December 2015 in the tea gardens of six districts (Tinsukia, Dibrugarh, Sivasagar, Jorhat, Golaghat and Dhemaji) of Assam. With 95% confidence interval and at 3.5% margin of error the required minimum sample size is 784. Taking 30% non-response rate and rounding up, the sample size becomes 1200. During the study, total 1204 numbers of samples were collected. These districts have the highest numbers of tea gardens of Assam. From each district randomly four tea gardens were selected. For sample collection health camps were organized in Tinsukia, Dibrugarh and Sivasagar districts. In the other three districts, the concerned doctors of the respective tea gardens helped to collect the samples. To make the residents of the selected tea gardens aware of the survey, letters were handed to the managers and doctors of all the selected tea gardens by the interviewers explaining the objectives of the study. Before sample collection, the interviewers explained about the objectives of the study to the participants. From each tea garden average 50 samples were collected. The age distribution of the study population was between 1 to 70 years. Blood samples were collected after taking informed consent from all the participants. Parental consent was taken in case of children below 16 years of age. A well-designed self-structured and validated proforma was used to get information on the ethnic group, any family history of blood disorders as well as to record all the laboratory findings. The study was approved by the Institutional Ethics Committee.

Patients who had received red blood cell transfusions in the 3 months prior to sample collection were excluded from the study.

All the participants received haematological screening for the presence of β-thalassaemia and other haemoglobinopathies in the Healthcare Clinical Biochemistry Laboratory of Assam Medical College & Hospital, Assam, India. After taking informed consent, 4 ml of peripheral blood was collected in K3EDTA vial from each participant. The samples were collected maintaining proper aseptic conditions. After collection, samples were transported to the laboratory in insulated packaging by maintaining refrigerated (+2^oC to +8^oC) condition with the help of gel packs. Complete Blood Count (CBC) was done in cell counter (SYSMEX XS- 800i, Japan) using standard procedure. High Pressure Liquid Chromatography (HPLC, Bio-Rad D10) was performed for all the collected samples.

A total of 1204 numbers of blood samples were collected and analysed. The whole study population consisted of tribals working in different tea gardens of the region. The distribution of haemoglobinopathies and β-thalassaemia among these ethnic groups; including the origin of these groups were shown in [Table/Fig-1]. The prevalence of β- thalassaemia was highest among the Munda ethnic group (3.07%) and the prevalence of HbS was highest among the Lohar ethnic group (4.73%) [Table/Fig-1].

During the study, haemoglobinopathies and β-thalassaemia were detected in 34.8% of the participants [Table/Fig-2]. The prevalence of haemoglobinopathies and β-thalassaemia found in the study population were shown in [Table/Fig-2]. The distribution of haemoglobinopathies and β-thalassaemia among different age groups were shown in [Table/Fig-3]. The age grouping for the study was done following WHO standard [15]. 1.66% of the participants were compound heterozygotes of β-thalassaemia which co-inherited with HbE and HbS. During the study 0.33% of homozygous HbE (HbEE) and 1.16% of HbE Trait (HbAE) cases were detected. Within the study population 27% cases had severe anaemia, 22% had mild anaemia and 39% had moderate anaemia. The data also revealed that the literacy rate was very low in this population [Table/Fig-4]. Within the whole population 30.23% were illiterate.

The high prevalence rate of haemoglobinopathy and β-thalassaemia could cause serious health and social problems among the tribals working in the tea gardens of the region. Preventing the birth of affected children is the best possible option for India to control haemoglobinopathies and β-thalassaemia [16]. A prerequisite for this is the knowledge of the prevalence of β-thalassaemia and other haemoglobinopathies in different regions of the country and particularly in different ethnic groups [16]. In India, marriages are usually arranged among individuals of the same caste or ethnic groups and so it is important to find out the prevalence of β-thalassaemia and also HbE among the different ethnic groups [16]. The current study was carried out to detect the prevalence of β-thalassaemia and haemoglobinopathies among the tribals working in the tea gardens of Assam based on their ethnicity. This study population is a distinct occupational group who migrated from states like Madhya Pradesh, Bihar, Orissa and Andhra Pradesh to work as tealeaf picker and have been residing within the tea-estates of the region [17,18]. The general incidence of β-thalassaemia trait and sickle cell anaemia varies between 3-17% and 1-44%, respectively in India [2,3]. The average sickle cell gene frequency was found to be highest 9.1% in Orissa, 7.4% in Madhya Pradesh, 7.2% in Uttar Pradesh and 7.1% in Tamil Nadu [19]. In upper Assam, the HbS gene frequency was 5.11% [11]. In India, the prevalence of Sickle cell trait (HbAS) varies from 5-40% among tribal populations from different states [20]. Among the four tribal communities of Visakhapatnam, HbAS distribution was 1.69% among Konds, 14.36% among Bagatas, 7.8% among Konda Doras and 13.59% among Konda Kammaras [20]. In Chhattisgarh, the prevalence of HbAS was 9.3% [21]. Studies done among the tribal groups in Orissa showed the prevalence rate of β-thalassaemia trait from 6.3% to 8.5% [22,23]. In the present study, 16.53% cases have sickle cell trait and 8.64% have β-thalassaemia trait [Table/Fig-2]. Another study from Orissa reported that the prevalence of HbAS was 5.3% among Kharia and Bhuyan tribe and the prevalence of β-thalassaemia trait was 6.2% in Kharia and 6.6% in Bhuyan [24]. The present study has shown that the prevalence of β-thalassaemia and sickle cell anaemia were highest among the Munda and Lohar respectively. According to our knowledge, this is the first study to report the presence of Hb E among the tribals working in the tea gardens of Assam [Table/Fig-1].

This study was also designed to provide information and awareness among the tribals working in the tea gardens about the genetic risks of having haemoglobinopathies and β-thalassaemia.

The present study has limitations as the study sites have not covered the whole state of Assam.

This study showed that sickle cell anaemia and β-thalassaemia were major health problem for the tribals working in the tea gardens of Assam. Therefore, the local government and the health departments have to develop a system of prevention and control program to decrease haemoglobinopathies and thalassaemia in this population. We suggested that prevention network of thalassemia should be established in this region, including establishment of a thalassemia database, haematological analysis laboratories, genetic counselling clinics, prenatal diagnosis centres and neonatal screening centres. Research in these areas should continue focusing on various challenges in care delivery, prevention and basic sciences on interaction of haemoglobinopathies with various other infections.