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November/December 2010 syzygy Laboratory Diagnosis of Dengue Infections SNP adds early diagnosis marker NS1 to dengue test panel Dengue cases worldwide continue to climb. It is the most common cause of fever in returned travellers. As well, outbreaks occur in the north of our state. The inability of serologic methods to reliably diagnose acute infections has been a serious impediment to quick identification of cases, and thus effective clinical case management, and the ability to intervene and implement outbreak control strategies. If the blood sample has been collected within the first five days of illness, dengue IgM may be negative. PCR has significantly improved this, although PCR is not always immediately available outside reference laboratories. In addition, serological diagnosis poses a number of pitfalls including cross-reactivity among other flaviviruses.* 'Original antigenic sin'** can complicate specific diagnosis of secondary flavivirus infections. IgM may be low or absent in secondary infection, and IgM may persist for 3 months or more following acute primary infection making accurate serological timing of infection difficult (Figure 1). To overcome these problems, the detection of a non-structural protein (NS1) present in the serum of infected individuals has been developed. The protein appears as early as the first day of the fever and is not inhibited by the development of dengue IgM antibodies. It peaks at around days 3-5 and subsides around day 9. The immune response to dengue virus infection can be considered in the context of primary versus secondary dengue infections (Figure 1). A primary infection describes the first dengue virus infection experienced by an individual. • NS1 antigen is produced from day 1 up to day 9 after onset of fever. • Detectable levels of IgM antibody will be produced by day 5 of infection, sometimes as early as day 3. IgM levels peak in 2 weeks, usually becoming undetectable at 2 to 3 months. • Low levels of IgG are detected in the early convalescent phase, and not during the acute phase. A secondary infection is a subsequent infection with a dengue serotype to which that person has not previously been exposed. A secondary immune response is generated. Such a response may also be triggered if a person has previously been exposed to a flavivirus (either through infection or vaccination) that is not dengue. • NS1 antigen is produced from day 1 up to day 9 after onset of fever. • The IgM response is more varied and often preceded by IgG. A minority of patients will show low or no detectable IgM levels. • High levels of IgG are detectable during the acute phase and reach levels above those found in primary or past infection. IgG may be detectable by day 3 of symptoms, and is generally detectable day 5-6. Levels persist for 30-40 days, then decline to levels found in primary or past infection. *Flaviviruses are arthropod-borne viruses. Those endemic in Australia and of clinical importance include dengue, the encephalitic group (Murray Valley encephalitis {MVE} and Kunjin) and infrequently the non-encephalitic group (Kokobera and Stratford). International travellers may encounter flaviviruses including dengue, Japanese B encephalitis (JE), West Nile virus (WNV), yellow fever and tickborne encephalitis. **'Original antigenic sin' is a secondary immune response which occurs when B lymphocytes are exposed to closely related but not identical antigens. The antibodies formed react more strongly with the antigen that elicited the primary response. For more information please contact Microbiologist on (07) 3377 8534 or email: [email protected] Figure 1 Aedes aegyptit is the vector for transmission of dengue infection. Photograph courtesy of Stephen Doggett (University of Sydney) patient care first Screening for Group B Streptococcus in Pregnancy The Safe and Effective Management of Warfarin Warfarin Care’s mission is to provide safe and effective management of patients on warfarin. We recognise that the referring doctor has primary clinical responsibility for the patient at all times and that we work in a collaborative arrangement to deliver high quality patient care with the best patient outcomes. As part of our proven effective strategies for managing Warfarin dosing in as safe a manner as possible, it is important that patients on Warfarin have a Full Blood Count and Liver Function Test done at sixmonthly intervals. This provides critical information on all patients for the doctors who perform the dosing and is particularly helpful when the patient‘s INR fluctuates or dosing requirements change. At your next consultation with the patient, and if your patient has not had these tests in the past six months, could you please provide them with a request for FBC and E/LFT. These tests can then be performed in conjunction with your patient's regular INR test. Along the same lines it is important that when SNP Warfarin Care manages your patient’s OAC therapy that all of the patient’s pathology should be performed with SNP. This allows the Warfarin Care doctors when determining the next Warfarin dose to access these results and be informed by them to provide the best dosing advice and patient outcome. Changes to any medication (including many types of prescribed, herbal and over-the-counter substances) are the most common causes of unexpected changes in the INR. As part of good management, the patient’s requirement for ongoing medication and their recent INR and other results should be reviewed at each visit to their doctor. The importance of good communication between all parties – patient, primary treating doctor and warfarin care doctor – cannot be stressed enough; your ongoing participation and interaction is essential in the safe delivery of this service. For this reason, we can accept patients onto the programme only if all these requirements are met. For more information please contact Dr Huong Phan FRACP, FRCPA on (07) 3377 8521 or email: [email protected] Group B Streptococcus (GBS) is a leading cause of early onset neonatal sepsis. Approximately 15-25% of women will be asymptomatic carriers of Group B Streptococcus of which, if left untreated one in 200 will have neonates that will develop neonatal sepsis. Guidelines for prevention of early onset neonatal GBS have recommended either a risk-based or screening approach to identify pregnant women for intrapartum antibiotic prophylaxis. For the screening approach, GBS carriage is best predicted by prenatal screening at 35-37 weeks gestation with a combined low vaginal and anorectal swab placed into a selective enrichment broth medium. Culture results are less predictive of status at term if performed at earlier gestations. This swab can be clinician collected or patient self-collected. Patient collection notes can be located at http://www.ranzcog.edu.au/publications/ statements/GBS%20SWAB%20SHEET3.pdf What to REQUEST – Group B Strep Screen clinical information – Pregnant/Gestation Specimen type – Combined anovaginal swab (can be self-collected) Swab type – Red top swab suitable for bacterial culture Reference: http://www.ranzcog.edu.au/publications/statements/C-obs19.pdf For more information please contact Microbiologist on (07) 3377 8534 or email: [email protected] PLAN NOW FOR WARFARIN CARE ENROLMENTS OVER CHRISTMAS 2010 Warfarin Care will be closed for new enrolments from 4 pm Wednesday 8 December 2010 and will re-open 8 am Tuesday 4 January 2011. This closure is necessary to allow the safe transfer of patients onto our program. For more information please contact our Warfarin Care team on (07) 3377 8578, or visit the 'Doctor Services' area at www.snp.com.au. Check our website www.snp.com.au closer to Christmas for an update on collection centre hours over the festive season. collection centre updates Brisbane Now Open REGIONAL Now Open Bellbowrie 8 Birkin Road Phone (07) 3432 9559 Mackay Oasis Plaza 118 Sams Road Phone (07) 4942 5747 West End 73-77 Russell Street Phone (07) 3846 6413 Geebung 328 Newman Road Phone (07) 3216 2014 Burpengary 33 Progress Road Phone (07) 3377 8747 Brisbane OPENING SOON Test Tip Faeces for Reducing substances Re-collections can be avoided by ensuring that samples for reducing substances are FROZEN immediately after collection by the patient and remain FROZEN during transportation to our laboratory. When samples are not frozen, the bacteria in the faeces consume the carbohydrates and give false negative results. Calamvale 2605 Beaudesert Road Phone (07) 3377 8747 Mudgeeraba 67 Railway Street (rear of building) Phone (07) 5559 1092 Peregian Shop 8 'Marguesas' David Low Way Phone (07) 5459 1400 REGIONAL relocated Noosaville (next door to Noosa Radiology) Shop 3.07a, 90 Goodchap Street Phone (07) 5474 3506 visit www.snp.com.au for pathology collection centre opening times Syzygy – now on 100% recycled paper Comments and Feedback? Contact us at [email protected] Sullivan Nicolaides Pathology recognises our corporate responsibility to respect and improve the environment in which we work and live. As part of our commitment to continually improve environmental performance and prevent pollution, Syzygy is now printed on 100% recycled paper.