Criteria for the Processing of Dengue Samples at the CDC Dengue Branch, San Juan, Puerto Rico
The diagnosis and treatment of dengue and dengue hemorrhagic fever are guided by the symptoms and findings that the patient presents, and cannot depend on laboratory confirmation, since routine tests can not confirm dengue with the speed required for patients in critical condition. The processing of samples for serologic diagnosis takes approximately one week, and the PCR results take approximately 3 days. Even so, it is necessary to eventually have a confirmation of the diagnosis, to exclude other etiologic possibilities, and to guide the follow-up of the patient's convalescence. The CDC Dengue Branch provides dengue testing free of cost to submitting physicians, state and private laboratories.
To obtain correct data on the spread of disease, adequately decide what laboratory tests to use, correctly interpret test results, and to assure that results get to the person who requested them, the following information is indispensable:
- Complete name, age and sex of the patient
- Home address
- Date of onset of symptoms
- Date that sample was obtained
- Complete name and mailing address of the physician, laboratory, clinic or hospital that the result should be sent to
Samples without the above-mentioned information, or written with illegible handwriting or with more than a month from date of sample collection to date of arrival at CDC, will not be analyzed.
The clinical samples that are processed weekly are of great importance to determine the serotype and genetic make-up of viruses being transmitted in the region, and to determine their geographic distribution. This information can be used to detect risk factors that may lead to a new and more severe pattern of disease, and to refine the clinical diagnostic ability of attending physicians. Diagnostic bleeding is not provided to persons referred to CDC.
In case of a severe dengue epidemic, CDC Dengue Branch will promptly analyze samples received with the minimum above-mentioned information. If number of specimens exceeds laboratory capacity, testing may be prioritized in the following order:
- fatal cases,
- cases in intensive care,
- hospitalized cases (with thrombocytopenia, hemorrhage, shock or hemoconcentration),
- all other cases.
We want to emphasize that to maintain efficient dengue surveillance, CDC will continue processing samples from outpatients and mildly ill persons any time of the year, and especially when dengue incidence in the island is relatively low (usually during the months from April to July).
Case Notification and Shipment of Samples of Suspected Dengue Cases
Dengue is characterized by an acute febrile picture accompanied by headache, retroorbital pain, body pain, often a rash, and other variable symptoms that can include obvious or mild hemorrhagic manifestations (such as a petechial rash) or hemoconcentration, shock or coma. This disease should be considered whenever there is an increase in the number of persons who go to the physician with an acute febrile illness, complaints of "monga" or "influenza," or an increase in the number of clinically diagnosed cases of German measles or regular measles.
Instructions for Obtaining and Handling Samples
- Once there is a clinical diagnosis of suspected dengue, take a blood sample (see #4 and #5) and fill out the Dengue Case Investigation Form [PDF - 409 KB]. With this Form you comply with the legal reporting requirement. These forms can also be obtained from the CDC Dengue Branch, the Regional Environmental Health Office of the Puerto Rico Department of Health. The form may also be photocopied without restriction.
- It is of great importance to fill out the Dengue Case Investigation Form in a clear and complete manner. The information received on each case (especially the date of onset of symptoms and date of sample collection) is crucial to select and interpret the laboratory analyses. Furthermore, a complete address makes it possible to identify the area where control measures should be implemented. Samples without the above-mentioned information, or written in illegible handwriting or with more than a month from date of collection to date of arrival at CDC, will not be analyzed.
- USA or the exterior, we recommend to freeze the serum immediately after separated and to send in dry ice. The case investigation forms and the acute blood sample should reach CDC Dengue Branch as soon as possible. They can be sent through the local Environmental Health office. The acute sample can be sent immediately; there is no need to wait until the convalescent sample is taken.
- To diagnose dengue, the laboratory requires a blood sample taken during the acute period of the disease and a second sample that can be taken from day 6 after the onset of symptoms. Informing the patient about the importance of coming back for a second sample, and giving an appointment for a specific day and hour, will increase the probability of obtaining the second sample. If the patient makes the first visit to the physician on or after day 6 after onset of the symptoms, that sample is enough. In that case, it is not necessary that the patient come for a second sample.
- Acute-phase samples (taken on or before day 5 after onset of symptoms), will be used mainly for PCR analysis in order to detect virus. Convalescent-phase samples (taken on or after day 6 after beginning of symptoms) will be used mainly for detection of IgM anti-dengue antibodies by enzyme-linked immunosorbent assays (ELISA). Differential diagnosis for dengue and WNV virus is available; but these tests need to be requested according to clinical presentation. Samples taken on days 4 and 5 of illness are of low yield for isolation as well as serology. WHENEVER THERE IS A HOSPITALIZED SEVERE CASE, PLEASE INDICATE IT IN THE CASE INVESTIGATION FORM.
Type of sample Interval Since the Onset of Symptoms Type of Analysis "Acute" until day 5
"Convalescent" 6 or more days
- Reports will be sent to the physician (if the return address has been indicated) with the results of positive, or clearly negative, cases. In cases with negative virus isolation, we will await a convalescent-phase sample before reporting a result.
- Results will be reported only to the laboratory or the physician who sent the sample (or an authorized secretary).
Dengue Branch, CDC
1324 Cañada St.
San Juan, PR 00920-3860
Tel. (787) 706-2399
Fax (787) 706-2496