BCG vaccine has existed for 80 years and has been proved highly useful in preventing severe TB infections. In China, neonatal BCG vaccination has become a routine as suggested by the World Health Organization. According to the literature, the incidence of BCG complication is less than 1% in immunocompetent hosts, most of which are presented as local lymph nodes diseases. 5, 6 However, there are concerns about the safety of BCG among PID patients including CGD. Deffert reported that in 297 cases of CGD patients with mycobacterial infections, BCG was most commonly identified in 220 (74%) patients, while TB was reported in only 59 (20%) patients.15 Francesca examined 71 patients with CGD from 20 countries and found 31 (44%) patients had tuberculosis, and 53 (75%) presented adverse reaction to BCG. 13 The BCG infection usually occurs in the first decade of life, especially within 1 year after vaccination, much earlier than the onset of TB. 16, 17 The finding was consistent with previous studies. In the research, BCG has a high incidence of complication and earlier onset than TB, with the earliest presentation of BCG disease 1 month after birth.
The impaired granulocytic phagocytosis would cause the infection to spread in the lymphatic and the blood system, with the lymphatic system being most vulnerable to infections. 11, 18 In the cohort, lymphadenopathy, whether regional or disseminated, was the most common feature. The most common location was in the left axillary ipsilateral to the injection site, followed by the ipsilateral cervical areas that develop along the lymphatic system. 19 The central abscess and rim enhancement could be regarded as a sign of progress, indicating caseous necrosis. After treatment, serial CT studies have been used to document the resolution of BCG-related lymphadenopathy, including changes in size and calcification, which are similar to the lymphadenopathy of tuberculosis.
Patients with PID usually have more severe BCG infection than patients without PID. Disseminated BCG involves multiple systems with fatal consequences in most cases. 17 The incidence is estimated to be 0.59 per 1 million and almost occurs in children with immunodeficiency disorders. 20, 21 The lung has been proved to be the most common site and may be the first involved visceral organ. However, the lack of typical imaging characteristics could lead to inaccurate diagnosis. 22–24 Nodules and exudation have been reported as the most common manifestations, and some are characterized by small nodular calcification in the pulmonary parenchyma and lymphoid nodes. 25 In the cohort, pulmonary lesions presented multiple manifestations, including granulomas forming pathologically characterized by multiple nodules and masses mainly in the bilateral lower lobes, bearing similarities with the infection of fungus like aspergillus and candida, while the incidence of calcification is relatively lower in the fungal infection. The regions of ground-grass opacity and consolidation vary from subtle patches to bilateral multi-segment distribution. Other lesions like interstitial pneumonia and fibrotic changes were local and mild without obvious volume loss.
In TB-endemic countries, children with CGD are at high risk of infection. In Argentina, Hong Kong, and Iran, up to 11%, 54.5%, and 31.7% of patients with CGD were found to have TB infection respectively. 25 We also observed a high incidence of TB in our cohort, most of which presented more severe infections than BCG group. Radiologic manifestations varied including heterogeneous patchy of consolidation, large masses with cavitation, multiple nodules, and obvious lymphadenopathy. Miliary disease has not been found in our group. Progressive fibrosis with volume loss and tractive bronchiectasis in the upper lobes occurred in almost 1/3 of patients, much severe than BCG. Lymphadenopathy is another feature of TB, which larger in size and most seen in the bilateral hilar area. Compared with TB infection, BCG lymphadenitis is more generalized and dispersed. TB mostly affects the elderly, and children below 15 years old only constitute less than 5% of all cases. 25–27 In the paper, the BCG group has a much younger average age than the TB group.
In CGD patients, mycobacterial Infection also affects other visceral organs in a disseminated pattern, with liver and spleen as the most common infected organs. 28 Hepatosplenomegaly and multiple small abscesses have been observed, unlike the abscess of other pyogenic infection. Osteomyelitis, central nervous system infection and intestinal involvement have also been reported in the published literatures, but with relatively lower morbidity. The bone infection of BCG and TB has similar radiographic appearance characterized by osteolytic destruction and periosteal reaction, usually in the epiphysis and metaphysis of the long bone. 29 In the small or irregular bones, osteolytic destruction and dilation can be found with soft-tissue swelling. 30, 31
As an attenuated live vaccine, BCG presents lower pathogenicity and better response to anti-tuberculous treatment than TB. However, BCG has a higher incidence, and BCG disease might be the first sign of CGD caused by mandatory vaccination after birth, earlier than bacteria or fungi. Therefore, it is suggested that an evaluation of underlying immunodeficiency should be given for infant and children diagnosed as BCG disease. 32 In addition, for neonate with a family history of PIDs, BCG vaccination should be delayed until PID is excluded.