Revisiting the timetable of tuberculosis

Abstract

Tuberculosis has a much shorter incubation period than is widely thought, say Marcel A Behr and colleagues, and this has implications for prioritising research and public health strategies

Fig 1

Incubation periods and cumulative percentage of patients developing primary infection or active TB in three different studies. A) Incubation periods are measured from the time of tuberculin skin test conversion to the first clinical indication of primary infection (n=130) and active TB (n=33), respectively. Data from Gedde-Dahl. B) Incubation periods are measured from the time of exposure to the first clinical indication of primary infection and active pulmonary TB, respectively (n=64 for each). Data from Poulsen. C) Incubation period of primary infection is measured from the time of tuberculin skin test conversion to the first clinical indication of primary infection (n=48). Incubation period of active TB is measured from the time of onset of primary infection to the development of active TB (n=106). Data from Wallgren.

Fig 2

Rates and incubation period of active TB in tuberculin positive (induration ≥5 mm) household contacts of patients with recently diagnosed TB. Half of the contacts were treated with isoniazid and half with placebo for one year, then observed for another 10 years. The total number of people for both groups was 13 176. Error bars show 95% confidence intervals. Data from Ferebee.

Fig 3

The incidence of active TB in 8838 British adolescents who were TST positive (≥15 mm induration) or TST negative, observed over 20 years, from 1951 to 1970 (top panel). The bottom panel shows the TB disease incidence rates for the same period in England and Wales. Data from Hart and Sutherland.

Fig 4

Time of onset of active TB in Asian immigrants to the UK, some of whom went to their home country and back to the UK before their onset of TB. A) Time of onset of TB in 128 immigrants who neither left the UK nor had known contacts with TB in the UK before receiving a diagnosis of TB. B) Time of onset of TB in 59 immigrants who visited their home countries and had no known contacts with TB in the UK before their diagnosis of TB. Time to onset is based on the time of initial UK entry. C) Same group shown (B), but with the time to onset measured by the time from re-entry into the UK after their Asian visits. Data from McCarthy.

Fig 5

Decreasing rates of TB in different age cohorts of men, based on the TB incidence rate declines for Norwegian men over a 10 year period, for the years 1946 to 1974. The incidence of TB decreased by around 60% in the same group of 40 year old men, from one decade to the next. During this period the annual rates of TB disease in young men were 2.5 to 6/100 000. Redrawn from original figure in Wiker et al.