BMC Infectious Diseases BioMed Central Research article Use of "biokit HSV-2 Rapid Assay " to improve the positive predictive value of Focus HerpeSelect HSV-2 ELISA

Background Commercially available assays to detect antibodies to the herpes simplex virus type 2 (HSV-2)-specific glycoprotein gG-2 have markedly improved serologic diagnosis of HSV-2 infection. However, even tests with high specificity can have low positive predictive values in low prevalence populations. HSV-2 is a chronic, life-long viral infection that requires both medical attention and potential alterations in health care strategy. As such, the concern for false positive diagnoses is high confirmatory testing is routine for other viral serologies such as HIV and hepatitis C. We evaluated such a strategy for HSV-2 serology by using an easily performed commercial test, biokitHSV-2 rapid test ("Biokit"; Biokit USA, Lexington MA) as a confirmatory test for the widely used gG-2 specific serology ("Focus;" HerpeSelect HSV-2 ELISA; Focus Diagnostics, Cypress CA). Methods We tested 782 sera by Focus HSV-2 ELISA, Biokit, and the current gold standard test, Western blot (WB). Results The positive predictive value of the Focus HSV-2 ELISA increased from 80.5% to 95.6% when Biokit testing was performed on sera that were initially positive by Focus HSV-2 ELISA. Confirmatory testing increased the specificity markedly among sera with Focus EIA values between 1.1 and 3.5: only 35% of low positive (index values 1.1–3.5) Focus HSV-2 ELISA results confirmed as positive by Biokit and WB compared with 92% of those with index values >3.5. Mathematical modeling of the data resulted in expected positive predictive values over 98% for populations with antibody prevalences typical of clinical practices in the US and Europe. Conclusion Confirmatory Biokit testing of positive Focus HSV-2 ELISA results is fast, easy, and effective in reducing falsely positive HSV-2 antibody results. Patients, clinicians, and laboratories could benefit from the enhanced specificity of this simple HSV-2 serologic test combination.


Background
Septicaemia is a common cause of paediatric morbidity and mortality. Deaths from paediatric septicaemia are likely to be higher in low-income settings. Children with septicaemia present with fever, difficult breathing, tachycardia, malaise, inability to feed or lethargy, but those with asymptomatic bacteraemia tend to show no obvious sign of illness. In Nigeria, septicaemia is a major cause of death in neonates and children [1,2]. The outcome of treatment of neonates with septicaemia has remained poor in Nigeria as shown by reports of mortality rate of 33% to 41% from two tertiary hospitals in the country [3,4].
Prompt diagnosis and effective treatment is necessary to prevent death and complications from septicaemia. Physical signs and symptoms are useful in identifying infants and children with septicaemia and other non-localised infections but these have limited specificity [5,6]. Clinical assessment using a combination of symptoms and signs are useful guides to provisional diagnosis of septicaemia. For instance, a seven-item, weighted, clinical score system comprising grunting, abdominal distension, increased pre-feed aspirates, tachycardia, hyperthermia, chest retractions and lethargy showed that these criteria were sensitive for identifying newborns with septicaemia [7].
Rapid immunological techniques like C-Reactive Proteins (CRP) assays may help in the preliminary diagnostic assessment of suspected septicaemia. However, they lack the capacity to detect specific pathogens. Bacteriological culture to isolate the offending pathogen remains the mainstay of definitive diagnosis of septicaemia. The results of bacteriological cultures and antibiotic susceptibility tests take about a week, necessitating initial empirical treatment of suspected septicaemia. Knowledge of epidemiological and anti-microbial susceptibility pattern of common pathogens in a given area helps to inform the choice of antibiotics. We report the pattern of bacterial isolates in children with clinical diagnosis of septicaemia seen at the University of Calabar Teaching Hospital in South-eastern Nigeria.

Methods
The study included all consecutive blood cultures in children aged 0-15 years admitted to the University of Calabar Teaching Hospital (UCTH) from July 1996 to December 2002. The indication for blood cultures were clinical features adjudged by the attending clinician to be indicative of sepsis especially fever without localized lesion and absence of asexual malaria parasite in peripheral blood. Presence of malaria parasitaemia did not preclude suspicion of septicaemia when illness was severe or risk factors of sepsis such as severe malnutrition, lethargy and abdominal distension were present.
Specimens were collected into cooked meat broth under aseptic conditions using sterile, disposable hypodermic needle and syringe and transported to the laboratory within 30 minutes of collection. Aerobic cultures were mounted on the same day and sub-cultured within 48 hours if there was any indication of growth. Eosin methylene blue and blood agar plates were used for sub-culture and incubated at 37°C aerobically and in candle extinction jar respectively. Full identification of organisms was done with standard bacteriological and biochemical methods [8]. Antibiotic sensitivity patterns of bacterial isolates were determined by agar diffusion method using antibiotic discs [9] Results A total of 1,201 children with suspected septicaemia were studied. The age and sex distribution of the patients are shown in Table 1. There were 539 (44.9%) females and 662 (55.1%) males. The majority of the patients were newborns (533; 44.4%) and infants (252; 21.0%).
Bacteria were isolated in 552 (45.9%) of the 1,201 patients studied. The types and pattern of bacterial isolates in age groups is shown on Table 2. The rate of isolation was highest among newborns (271/533: 50.8%). The overall rate of isolation reduced with increasing age but the types of organisms cultured did not vary with age. The most frequent isolates were Staphylococcus aureus (48.7%) and Coliforms (23.4%). Unidentified gram-negative rods

Discussion
The present study includes children of all age groups but neonates are in the majority (44.4%). It reveals a rather high rate (44.9%) of isolation of bacterial pathogens from blood cultures of children with provisional diagnosis of septicaemia. The isolation rate is comparable to rates reported in other studies of Nigerian neonates with suspected septicaemia in Calabar (50.6%) [10], Ilorin (30.8%) [11] and Ife (55%) [12].
In all these reports, the organisms were S. aureus and gram-negative rods (Pseudomonas aeruginosa and Escherichia coli). The present study shows a similar pattern. This observation is in consonance with reports from two other developing countries [6,13] This suggests that infections by these agents constitute a significant threat to child survival in this locale and other developing country settings.
The in vitro susceptibility tests of these two most common isolates (coliforms and S. aureus) showed high levels of resistance to such commonly used antibiotics as Ampicillin, Chloramphenicol and Co-trimoxazole. While 86.6% of S. aureus isolates were sensitive to Gentamicin, only 61.6% of coliforms were sensitive to the same antibiotic, showing higher levels of resistance than reported in the same hospital about a decade ago, which showed a sensitivity of 89.7% [10,14]. The local antibiotics policy informed by the result of that study recommends the use of gentamicin as the sole agent for initial therapy in neonatal septicaemia. This policy needs to be reviewed to include a third generation cephalosporin in keeping with the result of the present study.
Susceptibility of S. aureus to Erythromycin remains high in the current study (90.1%). Sensitivity of the few isolates of S. aureus tested against Azithromycin is 100%, comparable to the findings of another Nigerian study [11]. This highlights the variable nature of antibiotic susceptibility pattern both in time and location within the same country.
Susceptibility of coliforms and S. aureus to third generation Cephalosporins (namely Ceftazidine, Cefuroxime and Ceftriazone), and Azithromycin were quite good. A recent report from Pakistan, another developing country showed high levels of resistance of gram-negative organisms to ceftazidime (71.6%) and cefotaxime (55.2%) [13]. Improved commitment to rational use of these antibiotics in Calabar is needed to sustain this relatively high level of susceptibility.

Conclusion
This study has shown that S. aureus and gram-negative rods (Pseudomonas spp and coliform) are the leading causes of septicaemia in children in South-east Nigeria, a pattern similar to that of other low income countries. Observed decline in susceptibility of these common pathogens to common antibiotics calls for increased efforts to ensure more rational use of these drugs. Epidemiological surveillance studies such as the current one should provide useful information base to guide practice and policies on rational use of anti-infective agents.