Does 2x2 airplane passenger contact tracing for infectious respiratory pathogens work? A systematic review of the evidence

We critically appraised the literature regarding in-flight transmission of a range of respiratory infections to provide an evidence base for public health policies for contact tracing passengers, given the limited pathogen-specific data for SARS-CoV-2 currently available. Using PubMed, Web of Science, and other databases including preprints, we systematically reviewed evidence of in-flight transmission of infectious respiratory illnesses. A meta-analysis was conducted where total numbers of persons on board a specific flight was known, to calculate a pooled Attack Rate (AR) for a range of pathogens. The quality of the evidence provided was assessed using a bias assessment tool developed for in-flight transmission investigations of influenza which was modelled on the PRISMA statement and the Newcastle-Ottawa scale. We identified 103 publications detailing 165 flight investigations. Overall, 43.7% (72/165) of investigations provided evidence for in-flight transmission. H1N1 influenza A virus had the highest reported pooled attack rate per 100 persons (AR = 1.17), followed by SARS-CoV-2 (AR = 0.54) and SARS-CoV (AR = 0.32), Mycobacterium tuberculosis (TB, AR = 0.25), and measles virus (AR = 0.09). There was high heterogeneity in estimates between studies, except for TB. Of the 72 investigations that provided evidence for in-flight transmission, 27 investigations were assessed as having a high level of evidence, 23 as medium, and 22 as low. One third of the investigations that reported on proximity of cases showed transmission occurring beyond the 2x2 seating area. We suggest that for emerging pathogens, in the absence of pathogen-specific evidence, the 2x2 system should not be used for contact tracing. Instead, alternate contact tracing protocols and close contact definitions for enclosed areas, such as the same cabin on an aircraft or other forms of transport, should be considered as part of a whole of journey approach.

Effectiveness and outcomes of air travel-related TB incident follow-up: a systematic review

The World Health Organization (WHO) recommends following up passengers after possible exposure to a case of infectious tuberculosis (TB) during air travel. This is time-consuming and difficult, and increasingly so with higher numbers each year of flights and passengers to and from countries with high TB endemicity. This paper systematically reviews the literature on contact tracing investigations after a plane exposure to active pulmonary TB. Evidence for in-flight transmission was assessed by reviewing the positive results of contacts without prior risk factors for latent TB.A search of Medline, EMBASE, BIOSIS, Cochrane Library and Database of Systematic Reviews was carried out, with no restrictions on study design, index case characteristics, duration of flight or publication date.In total, 22 papers were included, with 469 index cases and 15 889 contacts. Only 26.4% of all contacts identified completed screening after exposure. The yield of either a single positive tuberculin skin test (TST) or a TST conversion attributable to in-flight transmission was between 0.19% (95% CI 0.13%-0.27%) and 0.74% (95% CI 0.61%-0.88%) of all contacts identified (0.00%, 95% CI 0.00%-0.00% and 0.13%, 95% CI 0.00%-0.61% in random effects meta-analysis). The main limitation of this study was heterogeneity of reporting.The evidence behind the criteria for initiating investigations is weak and it has been widely demonstrated that active screening of contacts is labour-intensive and unlikely to be effective. Based on our findings, formal comprehensive contact tracing may be of limited utility following a plane exposure.

Tuberculosis contact investigations associated with air travel in Ireland, September 2011 to November 2014

The risk of communicable disease transmission during air travel is of public health concern and has received much attention over the years. We retrospectively reviewed information from nine flights (≥ 8 hours) associated with infectious tuberculosis (TB) cases in Ireland between September 2011 and November 2014 to investigate whether possible transmission had occurred. Twenty-four flights notified in Ireland associated with sputum smear-positive pulmonary TB cases with a history of air travel were reviewed. Nine were suitable for inclusion and analysed. Six cases of infectious TB travelled on nine flights. A total of 232 passengers were identified for contact tracing; 85.3% (n = 198) had sufficient information available for follow-up. In total, 12.1% (n = 24) were reported as screened for TB. The results revealed no active TB cases among passengers and 16.7% (n = 4) were diagnosed with latent TB infection (LTBI) all of whom had other risk factors. Despite the limited sample size, we found no evidence of M. tuberculosis transmission from infectious passengers. This study identified challenges in obtaining complete timely airline manifests, leading to inadequate passenger information for follow-up. Receipt of TB screening results from international colleagues was also problematic. The challenge of interpreting the tuberculin skin test results in determining recent vs earlier infection was encountered.

Systematic review on tuberculosis transmission on aircraft and update of the European Centre for Disease Prevention and Control risk assessment guidelines for tuberculosis transmitted on aircraft (RAGIDA-TB)

As a setting for potential tuberculosis (TB) transmission and contact tracing, aircraft pose specific challenges. Evidence-based guidelines are needed to support the related-risk assessment and contact-tracing efforts. In this study evidence of TB transmission on aircraft was identified to update the Risk Assessment Guidelines for TB Transmitted on Aircraft (RAGIDA-TB) of the European Centre for Disease Prevention and Control (ECDC). Electronic searches were undertaken from Medline (Pubmed), Embase and Cochrane Library until 19 July 2013. Eligible records were identified by a two-stage screening process and data on flight and index case characteristics as well as contact tracing strategies extracted. The systematic literature review retrieved 21 records. Ten of these records were available only after the previous version of the RAGIDA guidelines (2009) and World Health Organization guidelines on TB and air travel (2008) were published. Seven of the 21 records presented some evidence of possible in-flight transmission, but only one record provided substantial evidence of TB transmission on an aircraft. The data indicate that overall risk of TB transmission on aircraft is very low. The updated ECDC guidelines for TB transmission on aircraft have global implications due to inevitable need for international collaboration in contract tracing and risk assessment.

Economics of United States tuberculosis airline contact investigation policies: a return on investment analysis

BACKGROUND

In 2011, the Centers for Disease Control and Prevention modified its 2008 protocol for flight-related tuberculosis contact investigation initiation. The 2011 Modified protocol was implemented and replaced the 2008 CDC protocol based on comparative epidemiologic and economic analyses; this publication reports the economic analysis results.

METHODS

A return on investment model compared relative changes in tuberculosis disease treatment costs resulting from expenditures on tuberculosis contact investigations and latent tuberculosis infection treatment for the 2008 CDC and Modified protocols.

RESULTS

At moderate/high rates of latent tuberculosis infection and tuberculosis disease, positive returns on investment indicated each $1.00 spent on tuberculosis contact investigations and latent tuberculosis treatment resulted in more than $1.00 of savings from reduced tuberculosis disease treatment costs. Low rates of latent tuberculosis infection and tuberculosis disease resulted in negative returns on investment, indicating economic losses from tuberculosis disease treatment costs. There were smaller economic losses at low latent tuberculosis infection and tuberculosis disease rates with the Modified protocol in comparison to the 2008 CDC protocol, while both identified comparable numbers of persons at risk for tuberculosis.

CONCLUSION

The Modified protocol for conducting flight-related tuberculosis contact investigations represents a better use of resources and protects public health.

Tuberculosis and air travel: a systematic review and analysis of policy

WHO international guidelines for the control of tuberculosis in relation to air travel require-after a risk assessment-tracing of passengers who sat for longer than 8 h in rows adjacent to people with pulmonary tuberculosis who are smear positive or smear negative. A further recommendation is that all commercial air travel should be prohibited until the person has two consecutive negative sputum smears for drug-susceptible tuberculosis or two consecutive cultures for multidrug-resistant tuberculosis. In this Review I examine the evidence put forward to support these recommendations and assess whether such an approach is justifiable. A systematic review identified 39 studies of which 13 were included. The majority of studies found no evidence of transmission. Only two studies reported reliable evidence of transmission. The analysis suggests that there is reason to doubt the value of actively screening air passengers for infection with Mycobacterium tuberculosis and that the resources used might be better spent addressing other priorities for the control of tuberculosis.

Tuberculosis investigations associated with air travel: U. S. Centers for Disease Control and Prevention, January 2007-June 2008

INTRODUCTION

Contact investigations conducted in the United States of persons with tuberculosis (TB) who traveled by air while infectious have increased. However, data about transmission risks of Mycobacterium tuberculosis on aircraft are limited.

METHODS

We analyzed data on index TB cases and passenger contacts from contact investigations initiated by the U.S. Centers for Disease Control and Prevention from January 2007 through June 2008.

RESULTS

Contact investigations for 131 index cases met study inclusion criteria, including 4550 passenger contacts. U.S. health departments reported TB screening test results for 758 (22%) of assigned contacts; 182 (24%) had positive results. Of the 142 passenger contacts with positive TB test results with information about risk factors for prior TB infection, 130 (92%) had at least one risk factor and 12 (8%) had no risk factors. Positive TB test results were significantly associated with risk factors for prior TB infection (OR 23; p<0.001). No cases of TB disease among passenger contacts were reported.

CONCLUSION

The risks of M. tuberculosis transmission during air travel remain difficult to quantify. Definitive assessment of transmission risks during flights and determination of the effectiveness of contact-tracing efforts will require comprehensive cohort studies.