Diagnostic performance of a novel ESAT6-CFP10 skin test for tuberculosis infection in school tuberculosis outbreak in China

Background

The ESAT6-CFP10 (EC) skin test is recommended by the World Health Organization for latent tuberculosis infection (LTBI). However, it is still unknown how the EC skin test performs in students during a school tuberculosis outbreak.

Methods

We conducted an epidemiological investigation to assess the performance of the EC skin test in this high-risk population.

Results

A total of 9 active student patients were confirmed in the same class as the index case, with an incidence rate of 18.0% (9/50). Among the 50 close contacts, 14 (28%) were over 15 years old and had a chest X-ray (CXR), and none of them had abnormal CXR findings. The rates of positive tuberculin skin test (TST) ≥ 5 mm and < 10 mm, ≥ 10 mm and < 15 mm, and ≥ 15 mm were 12.0% (6/50), 16.0% (8/50), and 10.0% (5/50), respectively. On the second screening, 44 students with the same class as the index case had the EC skin test, of which 31 (70.5%) had positive EC tests. All patients had negative sputum smear results, of whom 4 (44.4%) had positive Xpert results; three had a TST induration diameter between 5 mm and 10 mm, but all of them had an EC diameter > 15 mm; 5 (55.6%) had abnormal CXR results, but all the confirmed patients had abnormal CT results; Except for four cases that were diagnosed by Xpert, the remaining five were confirmed by CT scan.

Conclusion

The novel EC skin test performed well in students during the school tuberculosis outbreak. In some special conditions, such as when the index case is bacteriologically positive for tuberculosis and the rate of LTBI is higher than the average for the local same-age group, secondary screening is recommended 2-3 months after the first screening. Furthermore, we cannot ignore the role of CT in the diagnosis of early student tuberculosis.

High rate of transmission in a pulmonary tuberculosis outbreak in a junior high school in China, 2020

•

School tuberculosis outbreaks are common in China

•

Students with PPD ≥ 15 mm are recommended to have prophylactic treatment

•

More attention should be paid to students with PPD ≥ 10 mm and < 15 mm in school TB outbreaks

Background

School tuberculosis outbreaks are common in China. This study aimed to introduce a new screening process to help control outbreaks.

Methods

An epidemiological investigation into a school-based tuberculosis outbreak was conducted in order to identify the origin of the infection, and how it was transmitted.

Results

In total, 10 confirmed active tuberculosis cases were diagnosed among student contacts in the index case's class, giving an incidence rate of 19.2% (10/52). Three were found through a proactive visit and seven through screening. Of the nine secondary cases, two had purified protein derivation of tuberculin (PPD) ≥ 15 mm or blister (confirmed by computed tomography (CT) scan before preventive therapy), five had TST ≥ 10 mm and < 15 mm (two with abnormal chest radiography scan and three with positive T-SPOT tests, confirmed by CT) and two with PPD ≥ 5 mm and < 10 mm (confirmed by CT scan through proactive visit).

Conclusion

Further to our results based on this school outbreak, a new screening process is recommended that involves conducting interferon gamma release assays on those students with PPD ≥ 5 mm and < 15 mm if there are three or more active tuberculosis patients in the class with an epidemiological link. Furthermore, a CT scan is recommended for students who have had a recent tuberculosis infection before they have preventive therapy.

Diagnostic delay as main contributing factor to a large outbreak of tuberculosis in a university

OBJECTIVE

To describe the epidemiological characteristics of a large tuberculosis outbreak in the university environment and the main risk factors associated with it.

METHOD

A descriptive analysis of the data collected from sick individuals and their contacts was made. For the contact tracing, the guidelines established in the Tuberculosis Programme of the Autonomous Community of the Basque Country were followed. Six of the outbreak strains were sent to the National Centre of Microbiology for molecular typing.

RESULTS

The total number of cases of the outbreak was 11. The rate of tuberculosis infection in the classroom of the index case, including the sick individuals, was 88.1% (59 infected and only 8 uninfected). The diagnostic delay of the index case was 260 days, and in the other 8 symptomatic cases it ranged between 10 and 70 days. The pattern obtained by the 2genotyping techniques was identical in the 6 strains studied.

CONCLUSIONS

The long diagnostic delay of the authentic index case, which was diagnosed in the contact tracing, and the poor ventilation conditions of the classroom, determined the high number of secondary cases associated with this outbreak.

[Tuberculosis outbreak in a primary school: description and reflections on the value of gastric juice in the management of micro-epidemics]

AIMS

To describe a tuberculosis outbreak in a primary school arising from a secondary case.

METHODS

Contact study and clinical study of exposed patients. Chest x-ray, gastric aspirate processing, and clinical evaluation of all children with a positive tuberculin skin test (TST) were recorded. Differential diagnosis between tuberculosis disease (TB) and latent tuberculosis infection (LTI).

RESULTS

Two groups were identified: one of higher exposure to the index case (> 6 hours/day, for 3 months; n=17 children) and one of sporadic exposure (< 6 hours/day; n=82 children). Clinical or bacteriological criteria for diagnosing TB were seen in 6 out of 17 (35%) highly exposed children. Four of them had clinical or radiological criteria. The other two children were asymptomatic and had a normal chest X ray, but had a positive gastric aspirate for M. tuberculosis. The overall infection rate (TB+LTI) was 94%. One child out of 82 (1.2%) sporadically exposed children had radiological criteria for TB. Staff latent infection rate was 15%. Apart from the index case, there were no other tuberculosis cases among the staff. Relative risk (RR) of exposed children was 28.5 (95% CI: 3-250).

CONCLUSIONS

Prolonged exposure to a baciliferous patient may infect almost every child exposed in closed groups. It can also cause a high attack rate. In this scenario, routine gastric aspirate may be considered for all children with a positive TST. It may identify early subclinical TB with an increased probability of isolating the M. tuberculosis. The potential benefit of this isolation may reach the entire cohort.

Population-based contact investigation of a cluster of tuberculosis cases in a small village

A cluster of five cases of tuberculosis (TB) in persons aged 19-23 years who were not close contacts was detected in a small village in Spain in 2006. All culture isolates had the same chromosomal-DNA restriction pattern. Contact investigations of family members, friends, workmates and schoolmates were complemented with tuberculin screening offered to the resident population born between 1976 and 1995. Expanded contact tracing detected two new cases of TB, 27 tuberculin conversions and an excess of latent tuberculosis infections (LTI) in persons born between 1978 and 1990. The contacts of two cases had a significantly elevated prevalence of LTI. Two secondary cases of TB, 33.3% of those diagnosed with LTI and 47.8% of the converters were unaware of any contact with the TB cases, but had frequented some of the same bars. This study suggests that a considerable percentage of the episodes of TB transmission in young people may escape detection in conventional contact studies.

[The importance of genotyping of strains for the evaluation and interpretation of 5 school-based epidemic outbreaks of tuberculosis]

OBJECTIVE

The aim of this study was to describe 5 microepidemics of tuberculosis occurring in schools, establish the risk factors associated with the outbreaks, assess how well a concentric circles strategy for contact tracing predicts infection, and assess the usefulness of genotyping strains in the analysis of the outbreaks.

MATERIAL AND METHODS

The study assessed 5 epidemic outbreaks of tuberculosis using a standard contact tracing procedure. The outbreaks occurred in 2 day nurseries and 2 high schools between 1998 and 2005. Contacts were stratified using a concentric circle system based on level of exposure. DNA fingerprints of the available strains were determined based on the restriction fragment length polymorphism (RFLP) IS6110 and compared with the contact study to interpret the transmission of the infection.

RESULTS

We analyzed 5 outbreaks. Eighty-five contacts were analyzed in the first outbreak, 519 in the second, 116 in the third, 655 in the fourth, and 102 in the fifth. The rate of infection was 31%, 29%, 66%, 37.6%, and 32%, respectively. Secondary cases of active disease were detected: 9 in the first outbreak, 16 in the second, 5 in the third, 6 in the fourth, and 13 in the fifth. RFLP analysis revealed that a single strain was involved in 3 of the outbreaks, and in a fourth, at least 2 strains were involved. In outbreaks 2, 3, and 5, there was a significant association between the degree of contact and the probability of infection (P< .05). In all of the outbreaks, the relative risk of developing the disease was associated with the level of exposure.

CONCLUSIONS

Analysis of contacts based on concentric circles of risk predicts the likelihood of infection. RFLP facilitates analysis of complex transmission routes that are not detected using traditional methods of contact screening.