General Features of All Patients
From January 1, 2015 to December 31, 2020, a total of 134 patients who were diagnosed with BCG disease were enrolled. All of the patients had a clear history of BCG inoculation before the onset of the disease, and scars were visible at the vaccination site. Among all of the patients, 101 were male (75.4%). Most patients were from East China (n = 88 65.7%) around Shanghai followed by South China (n = 22 16.4%) and Southwest China (n = 12 9.0%). Almost all patients were lean, and the average BMI was 16.3 ± 1.8 (kg/m2). The median age at onset of BCG disease of all patients was 3.0 months old (IQR 1.67-4.0). The median age at diagnosis of BCG disease of all patients was 5.5 months old (IQR 4.5–8.6). Thus, a delay in BCG disease diagnosis was noted.
Genotype
Gene sequencing analysis of the 134 patients revealed that 112 cases (83.6%) had pathogenic mutations, whereas 22 cases (16.4%) had no mutations. Among the 112 PID patients, there were 55 cases of CGD (49.1%), including 53 CYBB gene mutations and 2 CYBA gene mutations; 28 cases of MSMD (25.0%), including 14 IL12RB1 gene mutations, 8 IFNGR1 gene mutations, 5 STAT1 gene mutations, and 1 IFNGR2 gene mutation; and 19 cases of SCID (17.0%), including 6 RAG1 gene mutations, 5 IL2RG gene mutations, 3 DCLRE1C gene mutations, 1 JAK3 gene mutation, 1 RAG2 gene mutation and 1 ADA gene mutation. There were 4 cases of combined immune deficiency (CID), including 3 CD40L gene mutations and 1 ZAP70 gene mutation. Some rare gene mutations were discovered, including 2 STAT3 gene mutations, 1 FADD gene mutation, 1 NLRP12 gene mutation, 1 FLG gene mutation and 1 KRAS gene mutation (Fig. 1). In total, we identified 19 types of gene mutations in 112 cases.
Clinical Manifestation in Different Groups
The number of rare genetic mutations was small and lacked homogeneity; hence, in this study, we did not compare patients with rare mutations with other patients. According to different types of gene mutations, we divided the remaining 124 patients into the CGD group, MSMD group, SCID group and unspecified pathogenic group. The sex composition ratio of the four groups was significantly different (P < 0.001). Almost all patients in the CGD group were males. The median ages at onset in the CGD group, MSMD group, SCID group and unspecified pathogenic group were 3.0 months old (IQR 0.6-4.0), 2.5 months old (IQR 1.5-3.0), 3.0 months old (IQR 3.0-3.9) and 3.0 months old (IQR 1.4–4.8), respectively. No significant difference existed among them (P > 0.05). The median age at diagnosis of the four groups was 6.8 months old (IQR 5.0-10.3), 4.5 months old (IQR 4.0-8.5), 5.3 months old (IQR 4.5–7.6) and 5.5 months old (IQR 4.3–6.5). Significant differences were noted among the four groups, and the CGD group had a significantly older age at diagnosis than the other groups (P = 0.019) (Table 2). Eighty-two out of 112 PID cases (73.2%) had a positive family history, and 19 out of 22 cases (86.4%) in the unspecified pathogenic group had a positive family history. No significant difference existed between them (P > 0.05). Every group experienced an evident delay in the diagnosis of BCG disease, especially the CGD group. Patients in the unspecified pathogenic group may have potential pathogenic gene mutations that require further study.
The most common clinical manifestations of the four groups were recurrent fever, abnormal vaccination site and left axillary lymphadenitis (Fig. 2). Patients also presented with cough, diarrhea, skin abscess, night sweats, abdominal pain, and hematochezia. Symptoms varied among the four groups. The CGD group and SCID group had a significantly higher rate of recurrent fever than the other groups (P = 0.003). There was no significant difference in the frequency of abnormal vaccination sites or left axillary lymphadenitis among the four groups (P > 0.05). Patients in the MSMD group manifested abnormal gait (2/28), which was due to BCG bone infection (Table 2).
Site and Severity of BCG Disease in Different Groups
The common BCG infection sites were the left axillary lymph node (104/134), BCG vaccination site (53/134) and lymph nodes except the left axillary lymph node (21/134), lung (13/134), skin (11/134), bone (10/134), digestive tract (6/134), blood (6/134), abdominal cavity (4/132), ear (3/134), spleen (2/134), liver (1/134) and thoracic cavity (1/134) (Fig. 3). Among all the patients, 15 cases (11.2%) were classified as local infections, 69 cases (51.5%) were regional infections, 19 cases (14.2%) were distant infections and 31 cases (23.1%) were disseminated infections.
In the CGD group, 7/55 (12.7%) patients had local infections, 28/55 (50.9%) had regional infections, 11/55 (20.0%) had distant infections and 9/55 (16.4%) had disseminated infections. In the MSMD group, 1/28 (3.6%) had local infections, 11/28 (39.3%) had regional infections, 3/28 (10.7%) had distant infections and 13/28 (46.4%) had disseminated infections. In the SCID group, 5/19 (26.3%) had local infections, 9/19 (47.4%) had regional infections, 1/19 (5.3%) had distant infections and 4/19 (21.1%) had disseminated infections. In the unspecified pathogenic group, none of the patients had local infections, 13/22 (59.1%) had regional infections, 4/22 (18.2%) had distant infections and 5/22 (22.7%) had disseminated infections. A significant difference in infection severity was noted among the four groups (P = 0.038). The MSMD group had a higher probability of disseminated infection than the other groups (13/28 [46.4%]). In the other three groups, regional infection was the most common type, accounting for 50.9%, 47.4% and 59.1% of patients in the CGD group, SCID group and unspecified pathogenic group, respectively. It is worth noting that the probability of developing disseminated infection in the unspecified pathogenic group was second only to that in the MSMD group (Table 3).
Coinfections in Different Groups
Apart from BCG infection, these patients often experienced recurrent infections caused by various pathogens, even in patients without PID. Tested samples were obtained from nasal mucosa, sputum, bronchoalveolar lavage fluid (BALF), pus of skin, stool, urine, gastric juice, blood steam and marrow. The common coinfections included fungi (43.5%); viruses, such as Cytomegalovirus (17.7%), Rotavirus (11.3%), human parainfluenza virus (10.5%), and Epstein‒Barr virus (7.3%); bacteria, such as Klebsiella (16.1%), Staphylococcus (6.5%), Enterococcus (5.6%), and Streptococcus (4.8%); and other pathogens, such as Mycoplasma (14.5%), Pneumocystis carinii (6.5%), parasites (1.6%) and Mycobacterium tuberculosis (1.6%). Fungal infections were very common in the four groups. The patients in the CGD and MSMD groups were mostly accompanied by bacterial infection, and the patients in the SCID and unspecified pathogenic groups were mostly accompanied by viral infection (Table 5).
Treatment and Prognosis in Different Groups
The median course of anti-tuberculosis treatment for all children was 7.0 months old (IQR 0.6–15). The MSMD group had the longest anti-tuberculosis treatment course at 34.5 months (IQR 9.8–51). The CGD group, SCID group and unspecified pathogenic group had treatment course durations of 7.0 months old (IQR 0.0–15.0), 5.5 months old (IQR 0.0–11.0) and 3.5 months old (IQR 3.0-7.8), respectively. No significant difference in anti-tuberculosis treatment courses was noted among the four groups (P = 0.130). Seventeen cases in the CGD group had completed hematopoietic stem cell transplantation (HSCT), of which 1 case was lost to follow-up, 13 cases were successfully transplanted (76.5%), 3 cases were unsuccessful. In addition, 13 cases in the SCID group had completed HSCT, and 11 cases were successfully transplanted (84.6%). There was no significant difference in the success rate of transplantation between the two groups (P = 1.000) (Table 2). At the end of follow-up, 80.7% of patients in the CGD group survived, 100% in the MSMD group, 88.5% in the SCID group and 89.5% in the unspecified pathogenic group. The median survival times in the four groups were 36.0 months (IQR 18.0–57), 26.5 months (IQR 7.8–35.0), 12.0 months (IQR 7.0-20.9) and 16.7 months (IQR 8.8–23.1) in the CGD group, MSMD group, SCID group and unspecified pathogenic group, respectively. No significant difference in survival time was noted among the four groups (P = 0.292). We wanted to know whether BCG disease severity affects prognosis, so we compared the patients in different severity grades in the CGD group. The results showed that there was no significant difference in survival time among patients with different infection severities in the CGD group (P = 0.925) (Fig. 4).