The traditional methods for diagnosis of fungal infections have been microscopy and culture, both of which have their limitations. Culture continues to be the gold standard. Although it is specific, culture has the disadvantage of being slow, and sometimes of low sensitivity especially in detecting candidaemia. Although quick in obtaining results, microscopy suffers greatly from non-specificity, and it is often not possible to put a name even to genus level. Hence, other modalities and new methods have been sought to address the above limitations. Some of these include antigen detection, PCR (or similar form of nucleic acid amplification) and serology. Issues to address are: 1. Detection of fungaemia and 2. Detection of important fungi (Candida, Histoplasma, Cryptococcus,Aspergillus species and Penicillium marneffei).By far the most common cause of fungaemia is candidaemia, an important cause of nosocomial septicaemia with mortality rate of 50-80%. Blood culture is notoriously insensitive (30%). Lysis centrifugation has been touted to give the best sensitivity for detecting candidaemia compared to other methods of blood culture. But recent studies show that the new BACTEC automated system, BacT-Alert system and even biphasic media are comparable to lysis centrifugation for detecting Candida species, but not as good for detecting Cryptococcus neoformans and dimorphic fungi. Non-culture methods have been tried - detection of d-arabinitol, enolase, 1,3 b-d-glucan and Heat Shock Protein 90, all of which are still not commercially available, and have their limitations. PCR has great potential for speed, species identification and drug susceptibility pattern, but suffers from high cost and a lot of practical and interpretative problems, and remains investigational.The only reliable and widely used serological test in mycology is latex agglutination for detection of Cryptococcus neoformans antigen. Cryptococcus neoformans can now be typed into var neoformans or var gatti by using CGB agar, or serotyped A through D using serotyping kits. Gene probes have also been available for diagnosis of Cryptococcus neoformans and the dimorphic fungi. However, culture isolates are required. It gives good sensitivity, specificity and quick same day results, but is expensive.In diagnosis of Aspergillus infection, antibody detection is not sensitive for invasive disease in immunocompromised host. Antigen detection has been so far in-house methods and there is a lack of a reliable rapid method. Penicillium marneffei, a recently recognised AIDS related opportunistic infection especially in Thailand, can be isolated from blood or various lesions by the standard culture method. Impression smears of skin lesions can give quick preliminary results. The realistic fact is that there has been much advances in diagnosis of fungal infection in recent years. Culture and microscopy remain the standard methods of detection, although they too suffer from limitations. It is hoped that new blood culture systems together with diagnostic biochemical and antigenic markers and molecular methods like PCR can be improved on, to complement culture methods in the early and specific diagnosis of fungal infection.
Full conference title:
6th Western Pacific Congress on Chemotherapy & Infectious Diseases
- WPCCID 6th