ABSTRACT

Tuberculosis (TB) remains the leading single microbial illness globally, with one-third of

the world’s population infected with Mycobacterium tuberculosis.

Pulmonary tuberculosis is the most common of all forms of TB and accounts for 70% of

all cases. In Nigeria, pulmonary tuberculosis is diagnosed by the sputum smear

microscopy after staining by Zehl-Neelsen method. The problems associated with the

diagnosis of TB using smear and culture techniques have necessitated the exploration of

the utility of serodiagnosis to support clinical suspicion of TB. Anti- M. tuberculosis IgG

antibodies may aid in the diagnosis of active M. tuberculosis disease. The aim of the

study was to test the diagnostic utility of the specific IgG serological assays for the

diagnosis of pulmonary TB. It was studied whether anti-M. tuberculosisIgG antibodies

are elevated in active M. tuberculosis disease. A diagnostic utility test of 184 participants

in which 92 were smear positive pulmonary tuberculosis cases and 92 were apparently

healthy controlswas conducted at the National Tuberculosis and Leprosy Training Centre

Saye and the Ahmadu Bello University Teaching Hospital, Zaria, Kaduna. All samples

were tested with theanti- M. tuberculosis IgG antibody assay. Of 92 patients with a

positive sputum smear microscopy test, 17 (18.5%) were positive for M. tuberculosis

antibodies. Eleven of the 92 (11.9%) controls were positive for M. tuberculosis

antibodies. The sensitivity of IgG ELISA tests was 18% and the specificity was 90%,

while the positive and negative predictive values were 66% and 53% respectively.

Although anti- M. tuberculosis antibodies can be detected in patients with active M.

tuberculosis disease, its detection may not be useful as an ideal adjunctive diagnostic

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CHAPTER ONE

1.0 INTRODUCTION

1.1 Background to the Study

Tuberculosis (TB) is caused by Mycobacteriumtuberculosis and remains a major global

public health problem responsible for over 1.5 million deaths in 2014(WHO, 2015).

Recent analysis of the global burden of TB revealed that Nigeria ranked third among the

22 high burden countries that account for 80% of the global TB epidemic with the highest

TB burden in the world (WHO, 2015). An efficient TB control program requires early

and accurate diagnosis and treatment of patients with active pulmonary TB.

A major obstacle to early treatment of TB is the lack of rapid accurate diagnostic

methods that can be applied in low-income areas. Diagnosis of active mycobacterial

infections     in     resource-constrained     settings     is     primarily     based     on     clinical

suspicion,radiological findings, and identification of acid-fast bacilli (AFB) in sputum by

smear microscopy. Microbiological culture requires specialized laboratories which are

costly and time-consuming.

TB most often affects the lungs, is curable, preventable and is spread from person to

person as aerosol. When people with pulmonary TB cough they propel the TB bacilli into

the air and common symptoms of active pulmonary TB are cough productive of sputum,

low-grade fever, hemoptysis, chest pain, weight loss and night sweats (Demkowetal.,

2007).

According to the global report on TB by the World Health Organization (WHO) in 2014,

1.5million people died from TB, including 400,000 among people who were HIV-

positive (WHO, 2015). The WHO estimates that 2 billion people are infected worldwide,

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and in 2014, there were an estimated 9.6 million incident cases of TB with 88% of these

occurring in HIV-negative patients and 12% in HIV-positive patients(WHO, 2015).

While the host’s immune system typically prevents the organism from spreading beyond

the primary site of infection, 5 to 10% of these latent M. tuberculosis infections progress

to active disease. Once the disease becomes active, it is contagious and lethal with a

mortality rate of greater than 50% in untreated individuals (Welch etal., 2012). Therefore,

early diagnosis of active TBis an essential step in the successful treatment through rapid

isolation of infected individuals and the early initiation of anti-TB therapy.

An issue of global concern presently is the emergence of drug-resistant TB, which is on

the increase in many countries of the world (WHO, 2015).The WHO recommended

strategy for global TB control is a short-course, clinically administered treatment (Rojas

et al., 2010; WHO, 2015).

A few studies have explored the role of serology in the early diagnosis of TB in Asia

(Maers, 2013). Serological tests detecting circulating antibodies against specific