Immigrants do not transmit tuberculosis more than indigenous patients in Catalonia (Spain)

Smoking cessation in tuberculosis patients and the risk of tuberculosis infection in child household contacts

BACKGROUND

While previous studies have shown that cigarette smoking increases the infectiousness of tuberculosis patients, the impact of smoking cessation on tuberculosis transmissibility has not been evaluated.

DESIGN/METHODS

Between 2009 and 2012, we enrolled 4,500 tuberculosis patients and followed 14,044 household contacts in Lima, Peru. Tuberculosis patients were classified into four categories: never smoked, quit in the distant past (stopped smoking >2 months prior to time of diagnosis), recently quit (stopped smoking ≤2 months prior to time of diagnosis), and active smokers. We used a modified Poisson generalized estimating equation to assess the risk of tuberculosis infection of child contacts at enrollment and by six months of follow-up.

RESULTS

In total, 1,371 (76.8%) child contacts were exposed to patients who had never smoked, 211 (11.8%) were exposed to distant quitters, 155 (8.7%) were exposed to recent quitters, and 49 (2.7%) were exposed to active smokers. Compared to child contacts of index patients who had never smoked, child contacts of recent quitters had a similar risk of tuberculosis infection at enrollment (adjusted risk ratio [aRR], 0.81, 95% CI, 0.50-1.32) and by six months of follow-up (aRR, 0.76, 95% CI, 0.51-1.13); child contacts of recent quitters had a significantly reduced risk of tuberculosis infection compared to contacts of active smokers (enrollment aRR, 0.45, 95% CI, 0.24-0.87; 6-month follow-up aRR, 0.48, 95% CI, 0.29-0.79).

CONCLUSIONS

Our results show that the adverse effects of smoking on the transmissibility of tuberculosis are significantly reduced shortly after quitting smoking, reinforcing the importance of smoking cessation interventions in tuberculosis control.

The role of super-spreading events in Mycobacterium tuberculosis transmission: evidence from contact tracing

BACKGROUND

In current epidemiology of tuberculosis (TB), heterogeneity in infectiousness among TB patients is a challenge, which is not well studied. We aimed to quantify this heterogeneity and the presence of "super-spreading" events that can assist in designing optimal public health interventions.

METHODS

TB epidemiologic investigation data notified between 1 January 2005 and 31 December 2015 from Victoria, Australia were used to quantify TB patients' heterogeneity in infectiousness and super-spreading events. We fitted a negative binomial offspring distribution (NBD) for the number of secondary infections and secondary active TB disease each TB patient produced. The dispersion parameter, k, of the NBD measures the level of heterogeneity, where low values of k (e.g. k < 1) indicate over-dispersion. Super-spreading was defined as patients causing as many or more secondary infections as the 99th centile of an equivalent homogeneous distribution. Contact infection was determined based on a tuberculin skin test (TST) result of ≥10 mm. A NBD model was fitted to identify index characteristics that were associated with the number of contacts infected and risk ratios (RRs) were used to quantify the strength of this association.

RESULTS

There were 4190 (2312 pulmonary and 1878 extrapulmonary) index TB patients and 18,030 contacts. A total of 15,522 contacts were tested with TST, of whom 3213 had a result of ≥10 mm. The dispersion parameter, k for secondary infections was estimated at 0.16 (95%CI 0.14-0.17) and there were 414 (9.9%) super-spreading events. From the 3213 secondary infections, 2415 (75.2%) were due to super-spreading events. There were 226 contacts who developed active TB disease and a higher level of heterogeneity was found for this outcome than for secondary infection, with k estimated at 0.036 (95%CI 0.025-0.046). In regression analyses, we found that infectiousness was greater among index patients found by clinical presentation and those with bacteriological confirmation.

CONCLUSION

TB transmission is highly over dispersed and super-spreading events are responsible for a substantial majority of secondary infections. Heterogeneity of transmission and super-spreading are critical issues to consider in the design of interventions and models of TB transmission dynamics.

Risk factors for infectiousness of patients with tuberculosis: a systematic review and meta-analysis

We performed a systematic review and meta-analyses of studies assessing tuberculosis (TB) patient-related risk factors for transmission of Mycobacterium tuberculosis infection. Meta-analyses were conducted for sputum smear-positivity, lung cavitation and HIV seropositivity of index patients with both crude and adjusted odds ratios (AORs) pooled using random effect models. Thirty-seven studies were included in the review. We found that demographic characteristics such as age and sex were not significant risk factors, while behaviours such as smoking and alcohol intake were associated with infectiousness although inconsistently. Treatment delay of >28 days was a significant predictor of greater infectiousness. Contacts of sputum smear-positive index patients were found to be more likely to be infected than contacts of sputum smear-negative patients, with a pooled AOR of 2.15 (95% confidence interval (CI) 1.47-3.17, I 2 = 38%). Similarly, contacts of patients with the cavitary disease were around twice as likely to be infected as contacts of patients without cavitation (pooled AOR 1.9, 95% CI 1.26-2.84, I 2 = 63%). In contrast, HIV seropositive patients were associated with few contact infections than HIV seronegative patients (AOR 0.45, 95% CI 0.26-0.80, I 2 = 52%). In conclusion, behavioural and clinical characteristics of TB patients can be used to identify highly infectious patients for targeted interventions.

Multidrug-resistant tuberculosis and migration to Europe

Multidrug-resistant tuberculosis (MDR-TB) in low-incidence countries in Europe is more prevalent among migrants than the native population. The impact of the recent increase in migration to EU and EEA countries with a low incidence of TB (<20 cases per 100 000) on MDR-TB epidemiology is unclear. This narrative review synthesizes evidence on MDR-TB and migration identified through an expert panel and database search. A significant proportion of MDR-TB cases in migrants result from reactivation of latent infection. Refugees and asylum seekers may have a heightened risk of MDR-TB infection and worse outcomes. Although concerns have been raised around 'health tourists' migrating for MDR-TB treatment, numbers are probably small and data are lacking. Migrants experience significant barriers to testing and treatment for MDR-TB, exacerbated by increasingly restrictive health systems. Screening for latent MDR-TB is highly problematic because current tests cannot distinguish drug-resistant latent infection, and evidence-based guidance for treatment of latent infection in contacts of MDR patients is lacking. Although there is evidence that transmission of TB from migrants to the general population is low-it predominantly occurs within migrant communities-there is a human rights obligation to improve the diagnosis, treatment and prevention of MDR-TB in migrants. Further research is needed into MDR-TB and migration, the impact of screening on detection or prevention, and the potential consequences of failing to treat and prevent MDR-TB among migrants in Europe. An evidence-base is urgently needed to inform guidelines for effective approaches for MDR-TB management in migrant populations in Europe.

Relating annual migration from high tuberculosis burden country of origin to changes in foreign-born tuberculosis notification rates in low-medium incidence European countries

The level of immigration from high tuberculosis (TB) burden countries (HBCs) which impacts on the foreign-born TB notification rate is largely unknown. In this work, we performed a cross-sectional analysis of epidemiological data from 2000 to 2013 from nine European countries: Austria, Denmark, Finland, Hungary, Netherlands, Norway, Spain, Sweden, and the United Kingdom. Crude notification rates were calculated for foreign- and native-born populations and a multiple-linear regression model predicting notification rates with HBC population data was generated. From 2000 to 2013, the population percentage with a foreign birthplace increased on average each year in all nine countries, ranging from +0.11%/year in the Netherlands to +0.66%/year in Spain. An annual increase in HBC migrants above +0.43% per year (95% Confidence Interval: 0.24%-0.63%) corresponded with higher TB notification rates in the foreign-born population of the countries analyzed. This indicates that migration from HBCs can exert a measurable effect on the foreign-born TB notification rate. However, an increase in the foreign-born TB notification rate coincided with an average annual rise in national TB notification rates only in countries, Norway (+3.85%/year) and Sweden (+2.64%/year), which have a high proportion (>80%) of TB cases that are foreign-born.

Genetic diversity of Mycobacterium tuberculosis isolates from foreign-born and Japan-born residents in Tokyo

Sequences of the full genomes of 259 clinical isolates of Mycobacterium tuberculosis, obtained from foreign-born and Japan-born patients in Tokyo, Japan, were determined, and a phylogenetic tree constructed by concatenated single-nucleotide polymorphism (SNP) sequences. The 259 isolates were clustered into four clades: Lineage 2 (East Asian or "Beijing" genotype; n = 182, 70.3%), Lineage 4 (Euro-American, n = 46, 17.8%), Lineage 1 (Indo-Oceanic, n = 23, 8.9%), and Lineage 3 (East African-Indian, n = 8, 3.1%). Of the 259, 36 (13.9%) were resistant to at least one drug. There was no multi-drug-resistant isolate. Drug resistance was greater for the strains in Lineage 2 than the non-Lineage 2. The proportion of Lineage 2 isolates was significantly smaller in foreign-born (n = 43/91, 47.3%) than in Japan-born (n = 139/168, 82.7%) patients, whereas the proportion of Lineage 1 isolates was significantly larger in foreign-born (n = 19/91, 20.9%) than in Japan-born (n = 4/168, 2.4%) patients. We also found eight SNPs specific to the typical Beijing sub-genotype in Lineage 2, including 4 non-synonymous SNPs. Of the 259 isolates, 244 had strain-specific SNP(s) and small (1-30-bp) insertions and deletions (indels). The numbers of strain-specific SNPs and indels per isolate were significantly larger from foreign-born (median 89, range 0-520) than from Japan-born (median 23, range 0-415) (p 3.66E-15) patients. These results suggested that M. tuberculosis isolates from foreign-born patients had more genetic diversity than those from Japan-born patients.