Detection of unsuspected cases of nosocomial transmission of tuberculosis by use of a molecular typing method

Analysing Tuberculosis Cases Among Healthcare Workers to Inform Infection Control Policy and Practices

OBJECTIVE

To determine the number and proportion of healthcare worker (HCW) tuberculosis (TB) cases infected while working in healthcare institutions in the Netherlands and to learn from circumstances that led to these infections.

DESIGN

Cohort analysis.

METHODS

We included all HCW TB patients reported to the Netherlands TB Register from 2000 to 2015. Using data from this register, including DNA fingerprints of the bacteria profile and additional information from public health clinics, HCW TB cases were classified into 4 categories: (1) infected during work in the Netherlands, (2) infected in the community, (3) infected outside the Netherlands, or (4) outside these 3 categories. An in-depth analysis of category 1 cases was performed to identify factors contributing to patient-to-HCW transmission.

RESULTS

In total, 131 HCW TB cases were identified: 32 cases (24%) in category 1; 13 cases (10%) in category 2; 42 cases (32%) in category 3; and 44 cases (34%) in category 4. The annual number of HCW TB cases (P<.05), the proportion among reported cases (P<.01), and the number of category 1 HCW TB cases (P=.12) all declined over the study period. Delayed diagnosis in a TB patient was the predominant underlying factor of nosocomial transmission in 47% of category 1 HCW TB patients, most of whom were subsequently identified in a contact investigation. Performing high-risk procedures was the main contributing factor in the other 53% of cases.

CONCLUSION

In low-incidence countries, every HCW TB case should warrant timely and thorough investigation to help further define and fine-tune the HCW screening policy and to monitor its proper implementation.

Infect Control Hosp Epidemiol2017;38:976–982

Factors associated with differences between conventional contact tracing and molecular epidemiology in study of tuberculosis transmission and analysis in the city of Barcelona, Spain

The aim of this study was to analyze the factors associated with conventional contact tracing (CCT) and molecular epidemiology (ME) methods in assessing tuberculosis (TB) transmission, comparing the populations studied and the epidemiological links established by both methods. Data were obtained from TB case and CCT registries, and ME was performed using IS6110-based restriction fragment length polymorphism (RFLP) analysis and mycobacterial interspersed repetitive unit 12 (MIRU12) typing as a secondary typing method. During two years (2003 and 2004), 892 cases of TB were reported, of which 687 (77%) were confirmed by culture. RFLP analysis was performed with 463 (67.4%) of the 687 isolated strains, and MIRU12 types in 75 strains were evaluated; 280 strains (60.5%) had a unique RFLP pattern, and 183 (39.5%) shared patterns, grouping into 65 clusters. CCT of 613 (68.7%) of 892 cases detected 44 clusters involving 101 patients. The results of both CCT and ME methods yielded 96 clusters involving 255 patients. The household link was the one most frequently identified by CCT (corresponding to 80.7% of the cases clustered by this method), whereas nonhousehold and unknown links were associated with 94.1% of the strains clustered by ME. When both methods were used in 351 cases (39.3%), they showed the same results in 214 cases (61%). Of the remainder, 106 (30.2%) were clustered only by ME, 19 (5.5%) were clustered only by CCT, and 12 (3.4%) were clustered by both methods but into different clusters. Patients with factors potentially associated with social problems were less frequently studied by CCT (P = 0.002), whereas patients of <15 years of age, most with negative cultures, were less frequently studied by ME (P = 0.005). Significant differences in the populations studied by ME versus CCT were observed, possibly explaining the scarce correlation found between the results of these methods. Moreover, ME allowed the detection of nonhousehold contact relationships, whereas CCT was more useful for tracing transmission chains involving patients of <15 years of age. In conclusion, the two methods are complementary, suggesting the need to improve the methodology of contact study protocols.

Nosocomial transmission of tuberculosis in two hospitals for mentally handicapped patients

BACKGROUND/PURPOSE

An unexpected significant increase in the number of tuberculosis (TB) cases in one hospital for mentally handicapped patients in eastern Taiwan was observed in early 2002. An active screening program was performed to identify undetected TB cases and to investigate nosocomial transmission of TB in two hospitals for mentally handicapped patients in eastern Taiwan.

METHODS

Active chest X-ray (CXR) screening followed by passive symptom screening were used to identify patients with pulmonary TB over 2 years in hospital A and B. IS 6110 restriction fragment length polymorphism and spacer oligonucleotide typing (spoligotyping) profiles of the isolates, clinical record of each case, TB control policies of the two hospitals, and risk factors of nosocomial transmission were analyzed.

RESULTS

A total of 94.8% (2298/2423) inmates in hospital A and 96.3% (1902/1975) inmates in hospital B were screened by CXR at the beginning of 2002. During the 2-year study period, TB was diagnosed by sputum cultures for 30 patients in hospital A (notified disease rate = 619 per 100,000 population per year) and eight patients in hospital B (notified disease rate = 203 per 100,000 population per year). Seventeen patients (56.7%) in hospital A had six cluster pattern strains, and none did in hospital B, which highlighted the importance of immediate expert consultation and thorough isolation of TB suspects.

CONCLUSION

This is the first study to prove that thorough isolation by referring patients to general hospital as soon as possible could decrease nosocomial transmission of TB in hospitals for mentally handicapped patients. Routine CXR screening at admission and maintaining a high alert for TB in daily practice are essential.

What is the outcome of targeted tuberculosis screening based on universal genotyping and location?

RATIONALE AND OBJECTIVES

Identifying and treating persons with latent tuberculosis (TB) infection (LTBI) at high risk for developing TB is part of the current TB elimination strategy. There are no specific criteria, other than medical risks, to designate groups as high risk for developing TB. We hypothesized that, if location-based screenings were done in communities where persons with genotypically clustered Mycobacterium tuberculosis resided, then persons with LTBI from recent transmission and with undiagnosed TB could be identified.

METHODS

Location-based TB screenings were done in partnership with multiple community-based organizations using resources previously used for other types of screening.

MAIN RESULTS

Location-based screenings identified one person with TB for every 83 screened, and one person with LTBI for every five screened. The yield of this targeted screening program for discovering persons with TB and LTBI exceeded what would be expected from nontargeted screening in a county with a TB incidence of 5.7 per 100,000 population.

CONCLUSIONS

Genotyping combined with geographic information systems analysis can potentially be used to define high-risk status and to define areas for location-based TB screenings.

Detection of dihydrofolate reductase genes by PCR and RFLP

The presence of plasmid-encoded trimethoprim resistant dfr genes is the most common mechanism responsible for the acquisition of trimethoprim resistance. The usual method to detect the presence of these genes is hybridization with specific probes. We describe an alternative, faster and easier method, based on PCR amplification and RFLP analysis, to discriminate up to sixteen different dfr genes.