Demographic characteristics and geographical distribution

A total of 71 cases of nocardiosis were collected, with ages ranging from 18 to 85 years and an average age of 56 years. Among these cases, 31 (43.6%) were aged 60 years or older, including 42 males and 29 females. The majority of the patients were farmers (67.6%, 48), and the main department involved was respiratory medicine (60.6%, 43). The most common specimen sources were sputum (52.1%, 37) and alveolar lavage fluid (46.5%, 33). Please refer to Table 1 for more details. The geographical distribution of Nocardia is depicted in Fig. 1. The city with the highest number of sources was Zhengzhou (21), followed by Zhoukou (12), Zhumadian (9), Shangqiu and Xuchang (6 strains each), and the classification of Nocardia species in various municipalities shows different.

Table 1 Basline characteristics of included patientsFig. 1

Geographical and spatial distribution of Nocardia isolates in Henan Province,China

Clinical characteristics

Among patients infected with Nocardia, 23.9% had a history of smoking, and 12.7% had a history of alcohol consumption. Out of 71 patients, 90.1% had at least one underlying disease. These included bronchiectasis (39), tuberculosis(16), type 2 diabetes (12), chronic obstructive pulmonary disease (COPD)(8), hypertension (8),anemia (5), coronary heart disease (3) and Sjogren's syndrome (1). During the diagnostic process for nocardiosis, 66 patients underwent complete imaging, where all CT scans revealed the presence of nodules or consolidative opacities. Lung cavity lesions were present in 24.2% of patients (16/66) and pleural effusions were observed in 31.8% of patients (21/66).Blood cell examinations were conducted on 65 patients. Among them, 33.8% (22/65) had elevated white blood cell counts, and 60% (39/65) had increased neutrophil proportions.CRP examinations were performed on 42 patients, and among them, 69% (29/42) showed elevated CRP levels. Additionally, among the 31 patients who underwent ESR examination, 24 had elevated ESR levels. Concurrent infections with other pathogens were present in 37 patients. These included 16 cases of Mycobacterium tuberculosis(MTB) infection, 5 cases of Aspergillus.spp infection, and 2 cases of non-tuberculous mycobacterium infection.Please refer to Table 1 for further details.

Molecular identification and distribution of Nocardia species

We initially identified the Nocardia species using MALDI-TOF MS and confirmed it further through 16S rRNA sequencing. However, the results of MALDI-TOF MS identification for the rare Nocardia species (N. africana, N.pseudobrasiliensis, N.flavorosea, N.amamiensis and N.rhamnosiphila) were inadequate and inconsistent with the sequencing results. Conversely, the identification results for N.cyriacigeorgica,N. farcinica,N. abscessus, N.beijingensis,N. otitidiscaviarum,N. asiatica,N. puris and N.wallacei were generally consistent between the two methods.

In the Additional file 1, we provide details of annual Nocardia isolates.The detection rate of Nocardia has exhibited an upward trajectory, increasing from a single isolate in 2017 to 20 cases in 2022. Among the 71 collected Nocardia isolates, a total of 13 species were identified. The predominant Nocardia species comprised N. farcinica(26.8%,9),N.cyriacigeorgica(18.3%,13),N.abscessus(11.3%,8), N.amamiensis (11.3%,8), N.otitidiscaviarum (7.0%,5)and N.beijingensis (7.0%,5). In our study, Nocardia strains were obtained using both traditional culture methods (BAP) and the MGIT960 culture method. Notably, there were disparities in Nocardia species detection between these two methods, as visually represented in Fig. 2. N. farcinica was the most frequently detected species via MGIT960 culture, while N. cyriacigeorgica predominated in traditional BAP culture.

Fig. 2

Distribution of Nocardia strains isolated by blood agar plate (BAP) culture and BACTEC MGIT 960 culture system (MGIT 960)

Antibiotic sensitivity

Table 2 provides a summary of Nocardia's sensitivity to 15 antibiotics, including the MIC inhibiting 50% (MIC50) and 90% (MIC90) of strains, along with the MIC range for all Nocardia isolates.It displays the sensitivity rate, intermediate rate, and resistance rate for each antibiotic. All Nocardia strains were 100% sensitive to TMP-SMX and linezolid. It is worth noting that different species of Nocardia demonstrate different antibiotic resistances, as shown in Table 2, N. farcinica has higher resistance rates to imipenem (47.4%), ceftriaxone (78.9%), tigecycline (78.9%) and clarithromycin (89.4%), while N.cyriacigeorgica has lower rates of resistance to imipenem(15.4%), ceftriaxone (15.4%), tigecycline (0%),and clarithromycin (23.1%) In addition, N. farcinica and N. abscessus exhibited different sensitivities to doxycycline and minocycline. One isolate of N. pseudobrasiliensis exhibited resistance to ceftriaxone, ciprofloxacin, doxycycline and minocycline, and intermediate susceptibility to imipenem, moxifloxacin, and amoxicillin-clavulanic acid.

Table 2 Antimicrobial susceptibility and MICs of 71 Nocardia isolates in clinical infections in Henan China from 2017 to 2023

The drug sensitivity results for each Nocardia species in this study were compared with the predicted antimicrobial drug sensitivity patterns provided by the CLSI standard M62 and larger-scale data studies. Table 3 showed a strong correlation between the drug pattern types and the identification of Nocardia species. Nonetheless, some differences were observed.For example, although only 52.6% of the cutaneous Nocardia isolates were sensitive to amoxicillin-clavulanate, the drug pattern indicated sensitivity according to the CLSI M62.The sensitivity rate of amoxicillin-clavulanate in N.abscessus complex isolates was only 43.8%, despite the drug pattern indicating sensitivity.The sensitivity rate of ciprofloxacin in N.otitidiscaviarum isolates was 20%, with the drug sensitivity pattern also indicating sensitivity.Furthermore, despite the sensitivity rate of 100% for amikacin in N.wallacei isolates, the drug sensitivity pattern indicated resistance.

Table 3 Main results of antibiotic susceptibility testing of clinical Nocardia isolates, derived from large-scale studies published beteen 2014 and 2023Comparison between pulmonary nocardiosis complicated with bronchiectasis group and non-bronchiectasis group

Bronchiectasis was found to be the predominant underlying disease among the patients based on the data presented in Table 1. The collected cases of nocardiosis were classified into two groups: the bronchiectasis group (39) and the non-bronchiectasis group(29), based on the patients' radiological examination results. We conducted a comprehensive comparison of the clinical characteristics, distribution of bacterial species, and drug sensitivity results between these two groups.Further detailed comparisons are provided in Tables 4 and 5.

Table 4 Characteristics of patients with nocardiosisTable 5 Nocardia species identification and antibiotic risistance

It can be concluded from Table 4 that there was no statistically significant difference in the distribution of age groups between the two groups (p > 0.05), but in terms of gender composition, the bronchiectasis group was predominantly female, whereas the non-bronchiectasis group was predominantly male. There was a statistical difference between the two groups in terms of smoking history, with patients with a history of smoking in the non-bronchodilated group being more susceptible to nocardiosis than those with a history of smoking in the bronchodilated group. In terms of comorbidities between the two groups, we learnt that patients with diabetes mellitus in the non-bronchiectasis group were more likely to develop nocardiosis. Other differences are detailed in Table 4.

In Table 5, our study found that there was a statistical difference between the two groups in terms of species distribution of Nocardia isolates, in both N.abscessus (p < 0.05) and N.farcinica (p < 0.05) detection rates, with patients with bronchodilatation being more likely to be detected with N. abscessus than those with non-bronchodilatation. In antibiotic susceptibility testing, there was a statistical difference between the two groups in ceftriaxone and tobramycin (p < 0.05) antimicrobial drugs.

Treatment and outcome

Out of the 71 cases of nocardiosis that were collected, treatment details were available for 61 patients, while the treatment plans for 10 patients were missing.Based on the data presented in Table 1, out of the 61 patients with treatment plans, 32 patients (52.5%) received combination therapy comprising of TMP-SMX. Among these patients, 10 received TMP-SMX combined with a single drug, while 22 patients received TMP-SMX combined with two or more antibiotics as part of a multidrug treatment plan.Moreover, 20 patients (32.8%) received a multidrug regimen containing amikacin and other antibiotics, while 20 patients (32.8%) received a regimen consisting of linezolid combined with other antibiotics. Furthermore, 24 patients (39.3%) were treated with a combination of quinolone antibiotics and other antibiotics, and 17 patients were prescribed alternative antibiotic regimens during the treatment. Out of the 71 patients' treatment outcomes, 3 patients were lost to follow-up with unknown treatment results, 58 patients (85.3%) achieved a cure or improvement in clinical symptoms, and 10 patients (14.7%) were discharged without being cured.