Page 16 - Delaware Medical Journal - March/April 2020

TABLE 1: Air changes per hour (ACH) and time required for removal efficiencies of 99% and 99.9% of airborne contaminants*
Minutes required for removal efficiency†
ACH
99%
99.9%
2
138
207
4
69
104
6
46
69
12
23
35
15
18
28
20
14
21
50
6
8
400
<1
1
* This table can be used to estimate the time necessary to clear the air of airborne Mycobacterium tuberculosis after the source patient leaves the area or when aerosol-producing procedures are complete.
† Time in minutes to reduce the airborne concentration by 99% or 99.9%.
Source: Guidelines for Preventing the Transmission of Mycobacterium tuberculosis in Health-Care Settings, 2005, Morbidity and Mortality Weekly Report, 2005
■ Close contact with someone with infectious TB disease;
■ A person who has immigrated from a part of the world with a high incidence of TB (any country outside the U.S., excluding Canada, Australia, New Zealand, or northern or western Europe);
■ Groups with high rates of transmission such as injection drug users, homeless persons, or those with HIV; and
■ Those who work or reside with people at high risk for TB in facilities such as homeless shelters, hospitals, and correctional facilities.
About half of all untreated LTBI cases who progress to TB disease will do so risk for progression exists in children under 4 as well as those with weakened immune systems, such as those with any of the following conditions:
■ HIV
■ alcohol or substance abuse, including
cigarette use
■ silicosis
■ diabetes mellitus
■ severe kidney disease
■ low body weight (<90% of their ideal weight)
■ head and neck cancer
■ immunosuppressive therapy such as tumor necrosis factor-
alpha antagonists, systemic corticosteroids equivalent to/greater than 15 mg of prednisone per day, or immunosuppressive drug therapy following organ transplantation.
TARGETED TESTING
Though it may seem counterintuitive, mass TB testing is not conducive to lowering overall TB incidence rates. According to the CDC, “unfocused population-based testing is not cost-effective or useful and leads to” false positives and inappropriate treatment with attendant drug treatment risks. TB screening “should be conducted only among high-risk groups, with the intent to treat if LTBI is detected.”8
Testing is warranted if a patient presents with symptoms of TB disease and risk factors
for exposure, or with an exposure that DPH

individuals). Otherwise, testing should not typically be done unless required for school or employment purposes.8 As a reminder, DPH does not conduct TB testing for pre- employment or school entry purposes. This can be done by any primary health care provider or most walk-in clinics.
64
Del Med J | March/April 2020 | Vol. 92 | No. 2