Discuss the Laboratory Diagnosis of typhoid fever.
Laboratory Diagnosis of typhoid fever.
Typhoid fever also called enteric fever is a syndrome mostly caused by Salmonella typhi which is gram negative, rod and motile enteric bacteria. This fever’s symptoms are fever, low pulse rate, headache, toxaemia, intestinal haemorrhage, constipation, bradycardia, enlarged liver and spleen. The infection is transmitted through fecal-oral contamination. The bacteria affects the small intestine by perforating them, and enters the bloodstream and lymphatics thus exerting the above effects and symptoms. This bacteria is one of the big five bacteria and has caused a considerable mortality and morbidity rate currently. Since the bacteria is highly infectious, the diagnosis of this organism is not carried out in routine laboratory diagnosis in Zimbabwe and requires better safety facilities. However, laboratory diagnosis in special laboratories make use of stool and urine specimens since the bacteria is found in small intestines and blood. Laboratory diagnosis of Salmonella typhi can be done using microbial and serological techniques.
In microbiology, culture and some biochemical techniques are used. Using culture techniques, the culture media of choice is Blood Agar (BA) and Xylose Lysine Desoxycholate Agar (XLD). Urine or Stool specimen is inoculated, streaked then incubated at 37°C in both anaerobic condition for one plate of Blood Culture and the other one in aerobic condition together with XLD for 18-24hours. Expected results are red colonies with black centres for the presence of Salmonella typhi on XLD while white non-haemolytic, smooth and white colonies are on BA. Gram stain can be carried out to confirm the identity of the bacteria and Salmonella typhi under the microscope is a red-pinkish and rod shaped (gram-negative bacilli). Motility test and the Hydrogen Sulphide production on Kligler Iron Agar can be done to further differentiate Salmonella species from Shigella species. Inoculation of single colonies from XLD on to motility medium and KIA followed by incubation at 37°C for 18-24hours is done. Black colouration on KIA and brown colouration of the whole motility media is indicative of Salmonella species. Antimicrobial sensitivity is carried out lastly in Muller-Hinton Agar to test for susceptibility or resistance of the bacteria.
However, serological tests such as the Widal test can be performed on patient serum to detect IgM type antibodies against O and H antigens specific to Salmonella typhi in a qualitative reaction. Quantitative analysis of these antibodies can be done using serial dilutions. Agglutination with known antigens specific to Salmonella typhi is indicative of the infection and its extent.
Clinical diagnosis is dependent on more than one test method hence clinically significant since there is an epidemic typhoid fever situation in Zimbabwe in Mbare which has a considerable mortality rate. Therefore, diagnosis including the above methods could have led to typhoid fever detection.
REFERENCES
Jawetz, Melnick and Adelberg’s Medical Microbiology by Geo F. Brooks, Karen C. Carroll, Janet .S. Butel, Stephen A. Morse, Timothy A. Mietzner 26th Edition 2013 The McGrawhill companies p238-242.
District Laboratory Practice in Tropical Countries by Monica Cheesbrough 2nd Edition 2006 Cambridge University Press.p45-62.
Diagnosis, Treatment and Prevention of Typhoid Fever in the Children of Bangladesh: A Microbiologist’s View by Samir K Saha, Ph.D. Department of Microbiology Dhaka Shishu Hospital Bangladesh
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