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SECTION 5 CLINICAL PRESENTATIONS OF TUBERCULOSIS

CHAPTER

29 Pulmonary tuberculosis in adults

Christopher J Hoffmann and Gavin J Churchyard

BACKGROUND

The World Health Organization (WHO) defines pulmonary tuber

culosis (TB) as tuberculous disease that involves the lung paren

chyma. Tuberculosis involving the trachea is often also included in

the definition. Extrapulmonary TB is disease involving any part of

the body other than lung parenchyma including other structures

within the thorax such as the pleura, pericardium and perihilar lymph

nodes. This distinction is most important from a public health per

spective because patients with untreated pulmonary TB pose an

infectious risk to the rest of the community, whereas the risk to the

community from extrapulmonary TB is minimal. Thus patients with

pulmonary TB who also have extrapulmonary involvement are clas

sified as cases of pulmonary TB by the WHO.

In addition to classification by location, TB has traditionally been

classified as primary or postprimary disease. Primary infection

includes the symptoms and complications arising from the first con

tact between host and the bacillus and is most clearly defined by

conversion from a negative to a positive tuberculin skin test (TST).

In the minority, the primary complex results in local progression or

distant disease; in the majority, the complex resolves. Postprimary

TB disease usually follows the primary infection by years, occurring

through reactivation or reinfection. Other nearly synonymous

terms with postprimary TB include reactivation TB, recrudescent

TB, endogenous reinfection and adult type progressive TB. In

years past, primary TB was considered a disease of children and post

primary TB a disease of adults. In the era of human immunodefi

ciency virus (HIV) distinctions between primary and postprimary

TB have become increasingly blurred as primary TB is often seen

in HIV infected adults.

This chapter focuses on the clinical presentation of pulmonary

TB and its complications. The classic presentation of primary and

postprimary pulmonary TB among HIV uninfected adults and

the atypical presentations of pulmonary TB associated with HIV

and other immunosuppressive diseases and drugs are described

along with the differential diagnoses. The impact of active TB

case finding on clinical presentation and its public health impor

tance is also included.

EPIDEMIOLOGY

A basic understanding of the epidemiology of pulmonary TB is

useful for estimating a patient’s or a population’s risk for pulmonary

TB. This is especially important when determining the most likely

aetiologies in building a differential diagnosis. In 2004, an estimated

9 million people had new TB diseases and 2 million deaths were

attributable to TB (see Chapter 3). Most new diseases and deaths

occurred in Asia and Africa, where 80% of all cases of TB occur.1

Of the 9 million new cases, three quarters were pulmonary TB.2

Multiple factors have contributed to the surge in TB that began

during the late 1980s and 1990s; immunosuppression from HIV is

the most dramatic. However, the impact of HIV on pulmonary TB

epidemiology is complex.

HIV contributes to pulmonary TB epidemiology in four impor

tant ways. Firstly, HIV associated immunosuppression increases the

risk of tuberculous disease, either from reactivation or from progression

of primary infection. Approximately 3–5% of adults with intact

immune systems develop TB disease within a year of initial infec

tion; subsequent lifetime risk of reactivation is 3–5%.3 Among

HIV infected individuals, nearly two thirds develop symptomatic

TB disease within the first few months of infection.4 As a result,

a disproportionate number of HIV infected individuals are diagnosed

with pulmonary TB.1

Secondly, individuals with HIV are at higher risk than HIV

uninfected individuals for recurrence of pulmonary TB from exog

enous infection.5 Thus, regions with both high HIV prevalence

and pulmonary TB incidence have a high proportion of the popu

lation highly susceptible to recurrence.

Thirdly, HIV coinfection accelerates progression of pulmonary

TB. As a result, HIV infected individuals typically progress to

death or diagnosis in a shorter time after developing pulmonary

TB than HIV uninfected individuals. Several recent studies have

estimated time to diagnosis by comparing incident pulmonary TB

cases identified in clinics with prevalent pulmonary TB identified

through community wide symptom and sputum screens. The esti

mated duration of pulmonary TB before development of signifi

cant symptoms ranges from 6 to 51 weeks among HIV infected

individuals and from 38 to 60 weeks among HIV uninfected indi

viduals.6–8

Fourthly, HIV coinfection diminishes the infectiousness of pul

monary TB. Although HIV leads to more rapid progression of

pulmonary TB, the burden of TB bacilli in the lungs is lower

among HIV infected individuals, leading to a lower rate of

sputum smear positivity.9,10 Among acquired immunodeficiency

syndrome (AIDS) patients with pulmonary TB, approximately

30–40% have smear negative disease compared with 20% smear

negative pulmonary TB among those uninfected with HIV.11

Smear negative pulmonary TB is 10 fold less transmissible than

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