TB, Airborne
Traveling XDR class.

Now the truth can be told: if I were the other night intern, I would have been taking care of the phthisic traveler a few days ago. Even though I didn't have the pleasure of putting on a mask and going into his room in Bellevue (sorry, "a New York hospital," as the first Times article coyly put it), I feel compelled to provide some information about a question we're all wondering about: how easy is it to get tuberculosis on an airplane?

You can't do that experiment. (Though it would be fun!) What does the literature say? Google Scholar gave me links to two articles. One of them talks about TB transmission from an infected crew member to his colleagues. The other, by Kenyon et al., is titled "Transmission of Multidrug-Resistant Mycobacterium tuberculosis during a Long Airplane Flight." We read in the abstract: "In April 1994, a passenger with infectious multidrug-resistant tuberculosis traveled on commercial-airline flights from Honolulu to Chicago and from Chicago to Baltimore and returned one month later. We sought to determine whether she had infected any of her contacts on this extensive trip."

In brief, their findings were as follows:

1. The researchers managed to get in touch with 802 fellow passengers, or about ninety percent of the people on the airplanes the woman traveled on -- a commendable effort.

2. Of these passengers, twenty-nine tested positive on the "TB skin test." Twenty-two of these had previous risk factors for tuberculosis, which means it's impossible to tell in this case (since the passengers weren't followed beforehand) whether their skin tests were positive before they ever took that flight.

3. Of the seven without previous risk factors for TB, six were on the longest flight the passenger took (a nine-hour jaunt from Chicago to Honolulu). They all sat in the same section, and four of them sat within two rows of the passenger.

The authors conclude, "The transmission of [the TB organism] that we describe aboard a commercial aircraft involved a highly infectious passenger, a long flight, and close proximity of contacts to the index patient."

How does this article relate to the now-famous globe-trotting lawyer? The kicker here is that the woman in the article was "highly infectious". To wit:
The index patient was a 32-year-old Korean woman, who according to relatives was taking no antituberculous medication but had previously been treated for tuberculosis — twice as an adolescent in Korea and once within the past two years in Japan — with unknown medication. She arrived in Honolulu in April on a tourist visa and was reportedly coughing and lethargic while staying with friends (Household 1) for five days. She then flew from Honolulu to Chicago and from Chicago to Baltimore, where she remained with friends (Household 2) for one month. Members of Household 2 reported a worsening of her symptoms, including progressive cough, lethargy, shortness of breath, fever, night sweats, and the eventual onset of scant hemoptysis. In May she returned to Honolulu, flying from Baltimore to Chicago and from Chicago to Honolulu. Eight days after returning to Household 1, she had an acute episode of hemoptysis, described as consisting of approximately 1 liter of bright red blood. Hospital evaluation revealed extensive pulmonary disease (Figure 1), and her sputum was highly positive (3+) for acid-fast bacilli and was culture-positive for M. tuberculosis. The patient died of pulmonary hemorrhage and respiratory failure five days after being hospitalized.

She died of TB shortly after the flights in question, and was highly infectious when she flew. Contrast this with the patient in this week's story, who has so-called "active" tuberculosis (the organism is in his blood) but does not appear to be either symptomatically ill or highly infectious (the amount of TB-causing organism in his sputum is low).

Was quarantining the passenger in this most recent case (or, rather, attempting to quarantine him) the right thing to do? Probably, since he is infected with so-called XDR (extremely drug resistant) TB, which is associated with a higher mortality rate. It's best to be on the same side, even though it's probably unlikely that anyone he traveled with got infected.

(However, I'll take the opportunity to mention that many organizations (schools and the like) use the TB skin test indiscriminately, without assessing their members' risk factors for TB, their infectiousness if they do test positive, and the resultant small likelihood of transmission even if they are infectious.)

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