ABSTRACT

Outbreaks of typhoid fever caused by Salmonella Typhi remains a serious health problem worldwide. There are several methods available for it diagnosis. However, misdiagnosis is usually experienced since most health care facilities rely only on Widal test. This study aimed at evaluating the performance of diagnostic tests, namely widal, stool and blood culture in the diagnosis of typhoid fever. Serum samples from 142 participants were subjected to Widal test. Likewise, Blood and stool samples from the same participants were analyzed for Salmonella Typhi infections using culture. The sensitivity (SE), specificity (SP), positive predictive value (PPV) and negative predictive value (NPV) for Widal test and stool culture was calculated. Comparison of categorical data was made using Chi square test. A P-value ≤ 0.05 was considered statistically significant.  Of the 142 screened participants, 18(12.7%), 1(0.7%) and 0(0%) were positive for typhoid fever based on Widal, stool and blood culture respectively. Comparative analysis of stool culture as gold standard against widal titration showed SE, PPV, SP and NPV of 100%, 87.9%, 5.6% and 100% respectively. The diagnostic cut-off titer of anti-O antibody was ≥1/320 and anti-H ≥160. Widal test is not reliable for the diagnosis of typhoid fever. The diagnostic cut-off of widal is comparable to stool culture. Typhoid diagnosis should rely most on stool culture to avoid over diagnosis and antibiotic misuse that often leads to resistance.

Keywords: Typhoid Fever, Diagnosis, Salmonella Typhi, Widal and Stool         Culture.

CHAPTER ONE

INTRODUCTION

1.1 Background to the Study

The genus Salmonella is gram negative, motile, non-lactose fermenting, non-spore forming rods and is facultative anaerobes [1]. Salmonella is one of the main causes of food and water born infections worldwide. Many Salmonellae species can infect gastrointestinal tract causing inflammations of the intestine leading to gastroenteritis [2]. Salmonella enterica serovar Typhi is well known agents of typhoid fever exclusively in human with incubation period of 7- 14days. Their transmission and portal of entry into the body is fecal-oral through ingestion of food, milk and water previously contaminated by fecal matter from patients or symptomatic carriers as the case of Typhoid Mary [1]. Typhi and paratyphoid fever has similar clinical manifestations which includes dry cough, anorexia, a dull continues headache, pyrexia, and abdominal pains and constipation.

Typhoid fever remains a major burden in the developing country amongst which is Cameroon. The burden of typhoid fever worldwide shows that it causes 16.6milion new infections and about 600000 deaths each year [3, 4]. Due to increase living standard, proper hygiene, sanitation, and better healthcare system in developed countries, the incident of typhoid fever has dropped to 10/100000 population \year, but the incident is still higher than 100/100000 population /year due to poverty, limited access to safe water and unhygienic practices in developing countries [1].

From a study carried out in the Northwest Region of Cameroon the prevalence of typhoid fever was 30.1% [5] and another study carried out at Deo Gratias Catholic hospital in Littoral region gave a prevalence of 68.7% [6]. This therefore implies that typhoid fever is endemic in most regions of Cameroon.

 Salmonella Typhi pathogens ingested in food survive passage through the gastric acid barrier and invade the mucosa of the small and large intestine and produce toxins. Invasion of epithelial cells stimulates the release of proinflammatory cytokines which induce an inflammatory reaction [7]. This inflammatory response causes diarrhea and may lead to ulceration and destruction of the mucosa. The bacteria can disseminate from the intestines to cause systemic disease [2]. Infections caused by S. Typhi and S. Paratyphi may involve serious complications and require treatment with antibiotics such as cefixime, chloramphenicol, amoxicillin, trimethoprim/sulfamethoxazole (TMP-SMX), azithromycin, aztreonam, cefotaxime or ceftriaxone to prevent death [8].

Effective vaccines exist for typhoid fever; these diseases are controlled by hygienic slaughtering practices and thorough cooking and refrigeration of food. In addition food workers and consumers should be educated about the need to cook meats, poultry, and eggs thoroughly and the need to wash hands and utensils with soap and water immediately after they have been in contact with raw meat, poultry, or eggs [9].

Accurate diagnosis of typhoid fever especially at early stage is important both for diagnosis of etiological agent and identification of individuals that may act as potential carrier. These carriers are solely responsible for acute typhoid fever outbreak [10]. The diagnosis of typhoid fever depends mostly on clinical signs and symptoms, serological markers, bacteria culture, antigen detection and DNA amplification. Blood culture is the most reliable diagnostic methods but it is expensive and most often some of this culture equipment are absent in some health care facilities.

In many African countries including Cameroon, Widal test is the most widely used test in the diagnosis of typhoid fever because it is relatively cheap, easy to perform and require minimal training and equipment. Although Widal test has been in use for more than a century, the value of the test in the diagnosis of typhoid fever is still debated for many years [11]. It classically relies on the demonstration of a rising antibody titer in paired samples 10-14days apart. In typhoid fever, however such a rise is not always demonstrable even on blood culture confirmed cases [12]. In addition, interpreting the test has been a problem because different cut-off has been reported from different places. Furthermore, patient management cannot wait for results obtained with a convalescent-phase sample. For practical purposes, a treatment decision must be made on the basis of the results obtained with a single acute-phase sample. So evaluating the result of a single Widal test is necessary for correct interpretation [13]. It is very important to note that some other related organisms share similar antibodies detected by Widal test. Consequently, it has been confirmed that normal healthy individuals without the history of typhoid vaccine (TAB) have high titers of Salmonella Typhi antibodies [14]. From the above observations typhoid fever diagnosis should not depend solely on widal test, it should be complemented with at least one standard method, this research is therefore aimed at comparing stool, blood culture and Widal test in the diagnosis of Salmonella infection among patients at the Buea Regional Hospital.

1.2 Statement of the Problem

There is an increase in misdiagnosis of Salmonella Typhi and drug resistance [1].  Widal test has been associated with some controversies which include inherent variability of the test, difficulty in establishing a steady-state baseline titer for the population, repeated exposures to S. typhi in endemic regions, and cross-reactivity with other non-Salmonella organisms. The test also relies on the demonstration of a rising titer of antibodies in paired samples 10 to 14 days apart in the diagnosis of typhoid fever. Moreover, patient compliance with convalescence test is difficult to achieve, and equally the laboratory scientist may not be aware of such test due to lack of proper training.

1.3 Rationale of the study

Typhoid fever is a disease which is endemic in most developing countries and its transmission depends mostly on the hygienic and sanitary condition of the area. Typhoid fever is responsible for pain and suffering on the local population. Typhoid fever has similar clinical manifestations with other febrile illnesses such as malaria and Dengue fever. Studies have also shown that some related organisms share similar antibody which is detected by Widal test which has been relied upon for several decades. These have caused misdiagnosis and mismanagement of the condition, which have induced unnecessary expenditure on patients and further impoverish the local population. These factors have led to high rate of inaccurate typhoid diagnosis, inappropriate antibiotic therapy and considerably multidrug resistance. This supports the need for proper isolation of the causative agents of suspected typhoid fever patients before antibiotic treatment to reduce further drug resistance and avoid patients spending for unnecessary test and treatment. This study will attempt to determine the short comings in the diagnostic methods of typhoid fever among febrile patients in Buea, Cameroon. As well as new treatment strategies that are alternative to the current one.

1.4 Research Questions

1) What is the performance of Widal test compared to various standard methods?

2) What is the cut-off value for Widal test in the diagnosis of typhoid fever?

3) What is the antibiotic susceptibility pattern of Salmonella Typhi isolates in febrile patients at the Buea Regional hospital?

1.5 Research Hypotheses

• Widal test has a poor performance.
• The diagnostic cut-off value for Widal test is comparable to stool and blood culture.
• They are increasing trends of resistance of Salmonella Typhi to antibiotics.

1.6 Research Objectives

1.6.1 General Objectives

This study aimed at evaluating the performance of Widal test compared to culture methods in the diagnosis of typhoid fever and to determine antibiotic susceptibility patterns of Salmonella Typhi isolates from patients at the Buea Regional Hospital.

  1.6.2 Specific Objectives

1. To evaluate the performance of Widal test and stool culture compared to standard methods in terms of sensitivity and specificity.
2. To determine the cut-off value of the Widal test in the diagnosis of typhoid fever, in comparison with blood and stool culture.
3. To determine the antibiotics susceptibility patterns of Salmonella Typhi isolates from patients at the Buea Regional Hospital.