Introduction

Typhoid / paratyphoid fever is caused by Salmonella typhi and Salmonella paratyphi A, B and C respectively. It is customary in our society that any feverish condition is first treated for malaria. If this fails, then treatment for typhoid automatically follows and if the patient at this stage fails to respond, it is only then that laboratory investigations are remembered⁽¹⁾. Salmonellosis is responsible for a variety of clinical syndromes, including gastroenteritis, enteric (typhoid) fever and extraintestinal manifestations.

Typhoid fever remains one of the most prevalent acute infectious diseases in the developing world including Nigeria. It continues to exist as an endemic disease due to poor (improper) sanitation and low socio-economic status of the people⁽¹⁾.

The Widal test (Widal’s agglutination reaction) is routinely employed for the serodiagnosis of typhoid fever by most Medical Laboratories in Nigeria. However, several workers within the Medical community have expressed doubt regarding the reliability of the test. There are several contributing factors for this uncertainty. Some have started calling for the discontinuance of Widal test as a diagnostic test for typhoid fever. Their argument is based on;

1. The difficulty of interpreting Widal test result in areas where typhoid fever is endemic and where the baseline titre of the normal population are not known.

2. The typhoid febrile agglutination test (Widal test) is often positive (raised O and H titres) in patients with infections caused by other bacteria, because of cross-reacting antibodies or previous vaccination with TAB or typhoid vaccine; chronic liver disease associated with raised globulin levels, and disorders such as rheumatoid arthritis, rheumatic fever, multiple myeloma, nephrotic syndrome, and ulcerative colitis.

3. The differential behavioural pattern of isolates of Salmonella species to various antibiotics as seen from our susceptibility test results.

The aim of this work therefore is to re-emphasize the importance of using appropriate specimens (faeces, urine and blood) in the laboratory diagnosis of Salmonella species and its antimicrobial susceptibility pattern prior to treatment for typhoid / paratyphoid fever.

Materials And Methods

A 5-year retrospective study on blood (Oxoid Signal blood culture system) and faecal cultures at the Medical Microbiology Laboratory of National Hospital, Abuja was carried out.

Blood Culture

The Oxoid Signal Blood Culture System (produced by Oxoid Limited, Wade Road, Basingstoke, Hampshire, RG24 8PW, England) was used to culture samples of blood collected from patients where the condition of bacteriaemia is suspected.

Figure 1

Figure i: Picture of Oxoid Signal Blood Culture System

Procedure for Blood Culture

Procedure for Faecal Cultures

Results

Blood Culture

Of the 2,818 blood cultures, only 90 (3.2 %) had positive cultures for Salmonella species.

Figure 2

Table i : Occurence rate of Blood species

Antibiotic Susceptibility Testing of Blood and Faecal isolates

Ten (10) antibiotic discs were used for the susceptibility testing. Viz; Amoxycillin, Ampicillin, Augmentin, Cefotaxime, Ceftazidime, Ceftriaxone, Chloramphenicol, Cotrimoxazole, Gentamicin, and Tetracycline.

Note:Only six (6) antibiotic discs are used for testing at any given time!

Figure 3

Table ii: Susceptibility Pattern of Blood isolates

Figure 4

Figure ii – Graphical representation of susceptibility pattern of blood Salmonellae isolates

Faecal Cultures

Of the 10,007 faecal samples cultured, only 159 (1.58%) had positive cultures for Salmonella species.

Figure 7

Figure iii – Graphical representation of susceptibility pattern of faecal Salmonellae isolates

Figure 6

Table iv : Susceptibility Pattern of Faecal isolates

Figure 8

Table v : Comparism of Antibiotic Susceptibility Pattern of Blood and Faecal isolates

Figure 9

Figure iv: Graphical representation of the comparism of antibiotic susceptibility pattern of blood and faecal isolates

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Discussion

Of the 2,818 blood cultures, only 90 (3.2%) had positive cultures for Salmonella species while the 10,007 faecal samples cultured had only 159 (1.58%) positive cultures for Salmonella species. Far away from Dong Thap Province, Mekong Delta Region of Vietnam, Lin et al; ⁽²⁾ reported blood culture Salmonellae positivity of 8.5%. Akinyemi et al; ⁽³⁾ reported a 16% blood culture positive rate from Lagos. Asuquo et al; ⁽⁴⁾ reported a 6% positivity of Salmonella species from blood samples in Calabar, Nigeria.

In 1995, Oboegbulam et al; ⁽⁵⁾ reported 16% positive stool cultures from suspected enteric fever patients in South Eastern Nigeria. However, in their report, Asuquo et al; ⁽⁴⁾ stated a 12.3% positive rate from stool cultures.

The sensitivity pattern in both blood and stool isolates show Ceftazidime (97.9% and 98.1%), Ceftriaxone (98.0% and 95.4%), Cefotaxime (97.6% and 93.7%), Gentamicin (80.9% and 78.5%), Augmentin (76.1% and 69.5%), Amoxycillin (45.5% and 56.4%), Chloramphenicol (40.6% and 75.2%), Tetracycline (100% and 51.1%), Cotrimoxazole (34.4% and 76.6%) and Ampicillin (35.3% and 32.6%).

The wide variation of susceptibility pattern in blood and faecal isolates for Chloramphenicol, Tetracycline and Cotrimoxazole cannot be explained.

Our results indicate a very low rate of typhoid / paratyphoid fever amidst varying susceptibility pattern of antibiotics to the isolates. The use of Widal agglutination test as a basis for diagnosing typhoid / paratyphoid fever and treatment of same based on a high titre value will definitely lead to drug misuse, emergence of drug resistant strains, as well as complications. Bacterial agglutination tests are often used to diagnose diseases in which the bacterial agent is difficult to cultivate in-vitro.

Agglutination tests for certain diseases such as typhoid fever have become less useful with the ability of most laboratories to cultivate and identify the causative agent. The typhoid febrile agglutination test (Widal test) is often positive in patients with infections caused by other bacteria, because of cross-reacting antibodies or previous immunization (vaccination) against typhoid. Appropriate specimens (stool, urine, or blood,) from suspected patients should therefore be cultured for the presence of salmonellae.