Contact screening and risk factors for TB among the household contact of children with active TB: a way to find source case and new TB cases

WHO has defined systematic screening for active tuberculosis (TB) as “the systematic identification of people with suspected active TB, in a preset target group, using tests, examinations or other procedures that can be applied swiftly” [1]. According to the published literature, a single pulmonary TB (PTB) patient can infect 10 to 15 persons on the average [2], having close contact, with in a community whereas 90% of the TB transmission in the community is due to sputum smear positive [3, 4]. Household contacts (HHC) are highly susceptible to acquire TB infection from the index cases because of their close proximity. The goal of contact tracing and their screening for TB could lead to the detection of additional cases of TB, maximizing the impact of case detection and effective treatment [5, 6]. The prevalence of TB disease is particularly soaring among children who are close contacts of a TB patient. Hence, screening children as contacts is generally recommended, though practiced in rarity [1].

Contacts of TB patients are at the greater risk of obtaining either TB infection or TB disease, depending on factors such as type of contact infectiousness of source case and environmental characteristics. In addition, host-related factors (age and immunology) additionally intervene with the likelihood of the patient getting to be infected or ill [7]. Enhanced learning of risk factors determining the possibility of contacts being infected with TB would reinforce contact investigations by enhancing prioritization so high-risk contacts can be focused on first.

Although screening and managing TB contacts are recommended, but not often done in low-income countries [8‐10]. A shortage of tuberculin, absence of chest X-ray (CXR) machines, lack of staff skill to figure out diagnostic results, minimum of 2 appointments needed to complete screening, transport and time costs for the patients and their families and high workload over healthcare workers have all been identified as barriers to screening [11]. Information on the contribution of routine contact investigations to early TB case detection is scarce in these countries.

Pakistan ranks fifth amongst the 22 high burden TB countries with TB incidence rate of 270 per 100,000 population and prevalence of 341 per 100,000 population; however, only 62% of these cases are detected and reported to the National TB Program (NTP) [12]. In Pakistan, passive case finding approaches were mostly used previously for TB case detection. Although, recently the NTP recommends use of active case finding in targeted population in order to enhance case finding [13], however, the practice is still limited in number of settings providing Directly Observed Treatment Short Course (DOTS) and only applied in screening contacts of TB adults. Nevertheless, there is very limited information on the value of contact investigation and approaches used in HHC screening of children with active TB in high incidence settings like Pakistan. The present study was aimed to evaluate the secondary TB cases and to investigate the risk factors in developing TB among the HHC of children with active TB.

Population based screening has been by and large discouraged by the reason of high cost, low efficacy and poor feasibility. Nevertheless, screening the targeted risk group might be more practical and cost-effective [18]. In the present study, 35 (1.5%) secondary TB cases were diagnosed with TB including 30 children aged ≤ 14 years. Total 19 (54.3%) cases of PTB- and 7 (20%) cases of PTB+ were identified among adults and children. In present study, only 9.3% of contacts were screened and 15.7% of these were diagnosed with TB. The proportions are low and need to be improved in future. Studies have reported that up to 22% of HHC have TB in high prevalence countries [19]. The low rates of contacts screened is possibly a repercussion of the passive nature of the program, which mainly depend on distinctive clinical symptoms being experienced by the contacts [18]. However, the high rate has been reported in a study conducted in South Africa, where a thorough investigation of HHC irrespective of symptoms resulted in detection of 17.4% of new TB cases [20].

In the current study, a significant number of contacts did not go for screening even when they experienced sustained cough. Reported foremost reasons for this were unawareness in respect to the need for screening, illiteracy and fear of additional cost of diagnosis and treatment. Majority of caregivers did not know that contacts with prolonged cough be in need of screening. Likewise, only some of them realized that young children ought to be screened in case of suspected symptoms and consequently children especially < 5 years of age are usually overlooked. The overall prevalence of TB among HHC was 1.5%. These results are comparable to recently published study from India [5]. In another study conducted in Uganda, 6% detection rate was reported among the HHC of TB index cases [21] with greater number in children than adults which is line with our findings. Recently published a meta-analysis across Africa, Asia and Middle-East has recorded a prevalence of 0.1–6.2% among the contacts screened by way of contact investigation [22]. If TB screening would have done systematically for all children in this study, we estimate that twice as many TB cases could be recognized.

First degree relatives are up to 5 times more inclined to cause infection in HHC [23]. In the present study, for source case, 63 of HHC were identified with 44 for having TB at present and 19 had during the past 2 years. Around 96.8% of the confirmed household source cases were adults with highest being mothers (39.7%) followed by fathers (27%). Our results are in agreement with the study from India where majority of the source cases were identified for adults [24] and particularly for parents [25]. Our finding for majority of the source as a mother is in agreement with the review article where a number of studies have mentioned that children whose source case is a female family member are at greater risk [11]. Results of a study from Pakistan has also reported increased number of mothers as the contact of children with active TB [26]. The most proper clarification of this fact could be that in Pakistan, like in many parts of the world, younger children are in closer physical contact with their mothers than their fathers and spend more time at home in close contact with females than males. In addition, the degree of exposure with TB contacts was assessed by recording the closeness of patients to the individual with TB within the household (in terms of time spend with TB contact). Contact of > 18 h per day with TB individual was significantly connected with TB among HHC. In numerous cases, prolonged contact occurred when the child or household is dependent on the individual with TB.

The researchers of one study conducted in South Africa, observed that children who were diagnosed with TB on CXR seemed to be asymptomatic [27‐29]. This shows that symptom based screening would miss some children with primary lung involvement on CXR. This study shows that the proportion of HHC of children with active TB screened under the current passive screening system of the NTP was very low. This is because the caregivers were asked to bring only the symptomatic contacts for screening. There could be possibility that not all the symptomatic contacts were attended at the treatment centres. In addition, there might be some asymptomatic contacts that could have TB infection. For that reason, the entire HHC of TB patient regardless of symptoms should be screened in order to have the early finding of additional cases of TB and to reduce TB transmission. This will increase the rate of detection for TB among the HHC of index cases and source case for child with TB.

Children, with a household source case and other caregivers especially grandparents or extended family members who take care of them were found at high risk of TB, which is in agreement with [30]. HHC of patient with TB have been reported at higher risk of infection than individuals in the general population. A number of modern studies conducted among children [31‐33] further confirmed that contact with a TB patient appeared as the paramount risk factor for TB infection. A statistically significant association of TB contacts was observed with age and gender as greater number of contacts were seen for children aged ≤ 5 years and female patients in the newly identified TB cases among the HHC. Similar results are reported from the studies conducted in Pakistan and Gambia [34‐36]. This shows the behavioural and cultural trend of study area where females (or girls) are confined to stay most of the times at home and less often get interaction with the people in community.

In the present study, host factors were not the exclusive factors associated with secondary cases of TB in HHC. Among the various environmental factors investigated, the cigarette smoke was found as significant risk factor of TB on multivariate analysis for the secondary TB cases. In accordance with WHO, smoking increases the risk of TB and > 20% of global TB incidence may be associated with smoking [37]. Exposure to tobacco smoke as significant predictors for TB infection among children of respective age has previously been reported by [38]. Furthermore, factors including children aged ≤ 5 years, overcrowding, living in shelter, and using water without boiling were observed as significant risk factors on univariate analysis.

Crowding reveals the increased likelihood of coming into contact with infectious persons expelling the bacilli in crowded environments supported by poor ventilation, recirculation as well as greater sharing of air [39]. These findings persisted in the current study where majority of patients (67.7%) were living in the houses with 1 to 2 rooms, 28.7% living in the shelters and 73.5% had > 6 family members reflecting the level of poverty and congested indoor environment. A study conducted in Pakistan, has presented the same level of living environment where 55% of children had to live in a single room house with families comprising 5 or more members [34]. Moreover, majority of these people were living in the areas with poor sterile conditions, poor cleanliness and more noteworthy communication among families and the neighbours which in turn increases the risk of getting and developing disease and infection at a more prominent rate. Howbeit, there is significance to HHC tracing, protocols must be confirming with the lifestyle of the target population. Frequent, intense contact with people outside the family is even more definite in crowded urban slums globally. In Pakistan, mostly children ride to school with 5 to 6 other children in an auto rickshaw designed for 3 on average. Public transports in these settings also carry far more people than there are seats. In the study area, children typically males aged 7 or more had practice to play outside in the streets most of the times which expose them to more contact in the community, hence making it difficult to identify the index case. Contact tracing procedures must therefore account for extent, closeness, and frequency of potential TB contacts further than household. Keeping all this in mind, the school-based TB-screening program at the study site would be beneficial in detecting early cases of TB. This strategy has been previously reported as cost-effective for detecting LTBI among children [40].

Giving the significance to screening contacts beyond the HHC, a study conducted in Pakistan in addition to 22.3% of TB prevalence among household has likewise watched extra 19.1% of predominance in close community [12]. As the strong evidence of close community investigation on TB case detection has been given by Aashifa et al., once the cost adequacy of close community investigation is set up, and the achievability of execution in to routine exercises is considered, community-based screening may grow across the country by the national program. Interventions like household visits by the health workers can provide an opportunity to educate family members and the community about screening HHC. Community education may possibly help parents on how TB presents in children, essentiality of screening and encourages accessing the healthcare at proper time. Additionally, further strategies to improve documentation of possible contacts should be given due consideration to increase the yield of contact investigation. Active case finding strategy should be initiated to have maximum case detection in family and neighborhood.

This study shows that the proportion of HHC of TB children screened under the current passive screening system of the NTP was very low. This is because the caregivers were asked to bring only the symptomatic contacts for screening. There could be possibility that not all the symptomatic contacts were attended at the treatment centres. In addition, there might be some asymptomatic contacts that could have TB infection. For that reason, the entire HHC of TB patient regardless of symptoms should be screened in order to have the early finding of additional cases of TB and to reduce TB transmission.