The importance of recent infection with Mycobacterium tuberculosis in an area with high HIV prevalence: a long-term molecular epidemiological study in Northern Malawi.
BACKGROUND
The proportion of cases of tuberculosis due to recent infection can be estimated in long-term population-based studies using molecular techniques. Here, we present what is, to our knowledge, the first such study in an area with high human immunodeficiency virus (HIV) prevalence.


METHODS
All patients with tuberculosis in Karonga District, Malawi, were interviewed. Isolates were genotyped using restriction-fragment-length polymorphism (RFLP) patterns. Strains were considered to be "clustered" if at least 1 other patient had an isolate with an identical pattern.


RESULTS
RFLP results were available from 83% of culture-positive patients from late 1995 to early 2003. When strains with <5 bands were excluded, 72% (682/948) were clustered. Maximum clustering was reached using a 4-year window, with an estimated two-thirds of cases due to recent transmission. The proportion clustered decreased with age and varied by area of residence. In older adults, clustering was less common in men and more common in patients who were HIV positive (adjusted odds ratio, 5.1 [95% confidence interval, 2.1-12.6]).


CONCLUSIONS
The proportion clustered found in the present study was among the highest in the world, suggesting high rates of recent transmission. The association with HIV infection in older adults may suggest that HIV has a greater impact on disease caused by recent transmission than on that caused by reactivation.
Department of Infectious Diseases, London School of Hygiene and Tropical Medicine, UK. judith.glynn@lshtm.ac.uk
Judith R
JR
Glynn
Amelia C
AC
Crampin
Malcolm D
MD
Yates
Hamidou
H
Traore
Frank D
FD
Mwaungulu
Bagrey M
BM
Ngwira
Richard
R
Ndlovu
Francis
F
Drobniewski
Paul E M
PE
Fine
D017088:AIDS-Related Opportunistic Infections / Q000382:microbiology*; D016000:Cluster Analysis; D015658:HIV Infections / Q000453:epidemiology*; D006801:Humans; D015994:Incidence; D008295:Malawi / Q000453:epidemiology; D017720:Molecular Epidemiology; D009169:Mycobacterium tuberculosis / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity; D012150:Polymorphism, Restriction Fragment Length; D015995:Prevalence; D014376:Tuberculosis / Q000453:epidemiology*