Study finds a higher percentage of TB patients with normal chest X-ray
29 Oct 2024
bySaras Ramiya
The study found that normal chest radiographic findings were five to six times more frequent in students aged ≤18.More than 40 percent of patients with positive Mycobacterium tuberculosis (MTB) culture and sensitivity test results had normal chest radiographic findings, shows a study.
The cross-sectional study on 56 patients with pulmonary tuberculosis (TB) revealed a higher percentage of normal chest radiographic findings compared to those reported in the national registry (9.9 percent). [Malays Fam Physician 2024;19:52, Int J Tuberc Lung Dis 2015;19(7):764-771] The patients were seen at the Kodiang Health Clinic (KHC) in Kedah, from April to October 2022 during a TB outbreak. In comparison, studies in an Asian country and a western country reported lower percentages of normal chest radiographic findings ie, 5.2 percent and 8.8 percent, respectively, among patients with culture-positive pulmonary TB. [Korean J Radiol 2010;11(6):612-617, Int J Tuberc Lung Dis 2008;12(4):397-403]
The KHC study is unique because the study authors analyzed the occurrence of normal chest radiographic findings among culture-positive pulmonary TB patients in an outbreak with varying epidemiological conditions and extents of TB transmission. Also, the differences in the study population as well as diagnostic criteria may have led to the disproportionate percentage. The study included all cases with a positive sputum acid-fast bacilli (AFB) smear due to the extended waiting time for the MTB culture and sensitivity test results. Quick diagnosis is crucial in managing TB outbreaks with the aim of successful disease control, the authors wrote.
In contrast, earlier studies were focused on certain populations like patients with advanced HIV-related immunosuppression. Only patients with positive MTB culture and sensitivity test results were included in previous studies.
The study found that normal chest radiographic findings were five to six times more frequent in students aged ≤18. This finding is corresponding to earlier studies, which showed Bacillus Calmette-Guérin (BCG) vaccination may protect children and adolescents against TB while reducing disease severity and reinstating chest radiographic findings. BCG vaccination is a routine vaccination provided to newborns in Malaysia having been initiated by the Ministry of Health in 1961. [BCG Revaccination. Available at https://www.moh.gov.my/index.php/database_stores/attach_download/347/147] Similarly, single patients were four times more likely to present with normal chest radiographic findings.
However, spouses of patients with smear-positive TB are exposed to and at a higher probability of developing pulmonary TB because of close contact. This leads to a higher bacterial burden resulting in more severe chest radiographic changes. This was confirmed in the KHC study where close contact did not significantly correlate with normal chest radiographic findings.
At the same time, the study found that asymptomatic patients had a 12-fold higher chances of having normal chest radiographic findings. This could be due to diligent screening of the community which gives rise to early detection of pulmonary TB even before symptoms were present. The lower bacterial load among asymptomatic patients is a likely explanation to normal chest radiographic findings.