The number of people infected with tuberculosis in sub-Saharan Africa has risen dramatically in the past 15 years, largely due to HIV infection. Bloodstream infection with Mycobacterium tuberculosis (mycobacteraemia) is a common cause of fever in sub-Saharan Africa, but diagnosis requires the help of specialists and a lengthy incubation period. Cheap and practical tests for eye disease such as the examination of the back of the eyeball (ophthalmoscopy) for choroidal granulomas could be an efficient alternative in the diagnosis of mycobacteraemia.

About 30 % of people who are infected with tubercle bacilli develop active TB if they are infected with HIV. TB is now the biggest cause of hospital admissions of HIV-positive people in Africa, but there is not much data on how simultaneous infection with HIV and TB affects the eyes. AIDS patients in Malawi and Burundi were examined for eye disease. Two-thirds had TB, yet they did not have the lesions typical of TB. The manifestations of TB in eye disease had not previously been studied with regards to mycobacteraemia.

In Africa the range of eye diseases caused by AIDS differs from that of developed countries – Cytomegalovirus (CMV) retinitis is not as widespread, yet herpes zoster ophthalmicus and conjunctival squamous cell tumours are more common. In AIDS patients the rates of HIV-related microangiopathy (disease of the small blood vessels), which is manifested as cotton wool spots (CWS) and small retinal haemorrhages, are higher.

A study looked at whether ophhthalmoscopy helped in the diagnosis of mycobacteraemia. All patients admitted with fever to a large hospital in Malawi were examined in an attempt to find out what signs of TB, HIV and AIDS were shown in the eyes and how pervasive these manifestations were. Patients underwent an eye examination, HIV tests, a chest x-ray, sputum examinations, bacterial and mycobacterial blood cultures and a malaria slide to check for parasites. The ophthalmoscopy was performed after dilation of patients' pupils with cyclopentolate and phenylephrine eyedrops.

The study made the following findings:

• Of the 307 patients examined, 36 % had TB, including 17 % with mycobacteraemia. HIV was present in 83 % of people and 62 % had AIDS. 94 % of TB patients were HIV positive.
• Using specialised blood culture techniques and prolonged incubation, a total of 53 patients (49 % of TB patients) were diagnosed with mycobacteraemia.
• Four patients had choroidal granulomas, all of whom had AIDS and three of whom had disseminated TB with mycobacteraemia. The fourth patient had a persistent fever but no other signs of TB. This was the first time that mycobacteraemia and choroidal granulomas had been linked.
• The research suggests that disseminated TB associated with HIV and immunosuppression is relatively highly prevalent.
• Among the AIDS patients, 17 % had microangiopathy visible in CWS and one had active CMV retinitis. The presence of microangiopathy was not related to TB.

Choroidal granulomas were present in only 2.8 % in TB patients admitted with fever. Thus ophthalmoscopy to examine fundi for choroidal granulomas was not a useful tool in determining whether patients have mycobacteraemia, but the presence of choroidal granulomas will confirm diagnosis of disseminated TB. AIDS patients in Africa rarely have CMV retinitis, possibly because they die relatively early on in the course of the disease. However, the low prevalence of CMV may also be due to differences of race, the HIV subtype or comorbidity.

Source(s):
‘Ocular disease in patients with tuberculosis and HIV presenting with fever in Africa’, British Journal of Ophthalmology, 86: 1076-1079, by N.A.V. Beare et al, 2002
'Clinical indicators of mycobacteraemia in adults admitted to hospital in Blantyre, Malawi', International Journal of Tuberculosis & Lung Disease 6 (12): 1067-74, by D.K. Lewis et al, 2002

Funded by: Malawi Health Support Fund of the Royal Netherlands Embassy in Lusaka; National TB Programme of Malawi; Foundation for the Prevention of Blindness, Liverpool, UK

id21 Research Highlight: 19 July 2004

Further Information:
Nicholas Beare
St Paul’s Eye Unit
Royal Liverpool University Hospital
Prescot Street
Liverpool L7 8XP
UK

Tel: 44 (0) 151 706 2000
Fax: 44 (0) 151 706 5905
Contact the contributor: nbeare@btinternet.com

St. Paul's Eye Unit, Royal Liverpool University Hospital, UK

Other related links:
'How many tests are enough? Testing for tuberculosis in Ethiopia'

'Test match: the search for a better test for TB infection'

'What's the diagnosis? Testing for tuberculosis in Kenya'

'Time lapse - delays in TB diagnosis in Zambia'

'Coughing up for TB tests - cost-effective diagnosis in Zambia'

See id21's collection of links relevant to infectious diseases.

See id21's collection of links relevant to HIV/AIDS.