Clinical criteria for post-epidemiological threshold phase DF diagnosis have been
largely employed in developing countries, due to the technical and economic difficulties
in carrying out specific tests to confirm DENV infection during outbreaks 23]. In these cases, blood-cell counts of patients with DF symptoms are the procedure
in healthcare institutions, as a way of monitoring disease evolution with the purpose
of preventing and treating the severe hemorrhagic form 24], 25]. Potentially, clinical signs and the hematological profile of patients with acute
DENV infection can vary individually and regionally, due to epidemiological characteristics,
such as the presence of other seasonal infectious diseases, host and virus genetic
background, and previous virus circulation, thereby making the use of only clinical
criteria for diagnosis questionable 26]. In order to investigate the effectiveness of such criteria applied to febrile patients
at the Marilia Hemocenter during the 2007 outbreak, demographic and hematological
status were assessed by applying a posteriori NS1-based DENV serological outcome data.
Through presenting high sensitivity and specificity in studies carried out in Brazil,
NS1 antigen detection has proved to be an important tool in early DF diagnosis 27]–30]. The kit employed in this investigation has an expected Positive Percent Agreement
(PPA) of 88.2 % (95 % Confidence Interval: 73.4–95.3 %) and a Negative Percent Agreement
(NPA) of 100 % (95%CI: 93.2–100.0 %) (manufacturer’s information). Accordingly, clinical criteria success
was confirmed in 70.6 % of the cases reported. The remainder (29.4 %) was comprised
of samples with a false DENV outcome or which corresponded to other infectious diseases.
In order to increase the accuracy of DENV NS1 serological diagnosis, the detection
of IgM/IgG DENV NS1 antibodies is recommended 31], 32]. However it was impossible to do so in the present study. Furthermore, serological
tests to check the presence of the different infectious agents were omitted here.
Even though indicator efficiency of hematological changes during progression in distinguishing
DENV from other infectious diseases is controversial, it remains essential in the
clinical management of DF and severe hemorrhagic dengue 25], 33]. Leukocyte and platelet counts below 3 760 cell/ml and 100 000 cells/ml, respectively,
and the presence of atypical lymphocytes, are commonly found in classical and severe
cases of DF 20], 34], 35]. Our data showed a strongly significant association of decreased leukocyte and platelet
counts in DENV+ patients. ROC curves reinforced LEU and PLA as the best factors for
predicting serological DENV outcomes (Fig. 1).
Biochemical liver damage markers, such as aspartate aminotransferase (AST), and serum
glutamic oxaloacetic transaminase (SGOT), as well as alanine aminotransferase (ALT)
and serum glutamic pyruvic transaminase (SGPT) serum levels, are used to evaluate
dengue disease severity 2]. However, in our health system these parameters are absent from the normal hematological
exam routine, and thus could not be included in the study.
Data of the demographic status of a population involved in a DENV outbreak facilitates
characterization of the epidemiological pattern of virus transmission, thereby contributing
towards prevention and management. In Asia, where the number of severe hemorrhagic
dengue cases is the highest in the world, with a fatality rate of 3.5 %, prevalence
is higher in children under-15 36]. In the 2007 Marilia DENV outbreak, the adult population was mostly affected by DF,
with only five cases of the non-lethal hemorrhagic form of the disease (0.4 %). No
differences in gender or age were found among DENV+ and DENV- patients. This DENV
transmission pattern is the most common in the Americas 9].
In the different regions of Brazil, the time span of DF outbreaks after the establishment
of an epidemiological threshold, is long-lasting, and can continue throughout the
hot rainy season. In São Paulo State it can last for four to six months 37]. During this period, health care facilities are overcrowded and there is confusion
in diagnosis with seasonal diseases. Moreover, and depending on the course of infection,
it is possible that hematologic changes, so commonly associated with the more severe
DENV diseases are not very evident in initial data. Thus, in order to further adapt
monitoring of the disease, all patients suspected of DENV infection are assayed for
hematological changes 38]. By taking into consideration the regional demographic and hematological profiles
of DF and its more severe hemorrhagic form 39], 40], the early definition of these characteristics can improve management efficiency.
Thus, in order to guarantee maintenance of parameters throughout the 2007 Marilia
outbreak, the patients were divided into four temporally consecutive subsets for comparative
analysis. The results indicated temporal homogeneity in demographic and hematological
profiles, especially brought into evidence by logistic regression and ROC curves (Table 3 and Fig. 2). This showed LEU and PLA |to be independent factors associated to DENV serological
positive diagnosis during the whole period.
There was also a statistically significant association of hematological variables
in all DENV serological positive samples (Table 5), compatible with DENV infection laboratory findings 37]. However, certain differences were found by additive logistic regression analysis,
when comparing the entire dataset and subsets s1 to s4 (Tables 4 and 6). The most significant difference occurred in subset s3, which presented high correlations
with DENV positive serological diagnosis. This difference could be attributed to specific
unidentified features related to sampling during the period, since this was the only
statistical significant variable to be associated to DENV diagnosis.
Currently, methods for the specific treatment and effective prevention of DENV infection
are still unavailable. Furthermore, a specific and sensitive method for early DENV-diagnosis
is not accessible to all the regions and patients during the course of long dengue
epidemics in developing countries, this including Brazil. In order to improve dengue
management in this situation, an alternative strategy used by public health care institutions
in São Paulo State is, according to the size of the population, determine an epidemiological
threshold after the epidemic has reached the incidence rate. Before this, patients
undergo dengue laboratory diagnosis. Considering our results, if the epidemiological
and hematological profile patterns of the dengue-affected part of the population are
investigated in the beginning of the outbreak, when specific diagnosis is carried
out after the threshold is reached, the resultant hematological profiles could be
used with more accuracy to improve disease management. Furthermore, to reduce the
number of dengue false-positives from exclusive clinical-criteria diagnosis, individuals
notified as being infected but presenting high scores for LEU and PLA, could be submitted
to dengue serological testing. Thus, definition of the epidemiological pattern of
DENV transmission in regions with recurrent outbreaks could help healthcare institutions
to prevent virus spread and manage associated diseases.