Is there an inapparent dengue explosion?

Abstract

Authors' reply Sir—We agree with Scott Halstead that many dengue infections are clinically inapparent, and their frequency varies with the strain of virus and the epidemiological circumstances. Dengue infection causes a spectrum of illness ranging from truly inapparent infection, through mild viral syndrome and classic dengue fever, to DHF. As a result of poor surveillance, many clinically mild dengue infections are not reported as dengue fever but as malaria or viral syndrome. Annual global reports of dengue cases to WHO averaged over 340 000 for 1991–95.1WHODengue haemorrhagic fever; diagnosis, treatment, prevention and control. 2nd edn. WHO, Geneva1997Google Scholar Most locations, even with good reporting, will have a ratio of diagnosed to reported dengue fever cases of at least 10/1, and in many areas (owing to mild cases, misdiagnosis, and difficulties of reporting), the ratio of dengue fever cases with symptoms to those actually reported may be higher than 100/1. In view of the poor surveillance for dengue fever in most countries, the high frequency, and expansion of epidemic dengue in past years, we believe that the estimate of 50–100 million aanual cases of dengue fever is valid. Case fatality rates are the ratio of fatal cases to the number of patients with the illness (usually expressed as a percentage). Halstead cites case fatality rates that refer to groups of patients that differ from the group we examined. The rates he cites for Asian nations (0·05–3·5%) represent the number of deaths per 100 cases of DHF or dengue shock syndrome (DSS). The case fatality rate for Cuba in 1981 (1·5%) represents the number of deaths per 100 dengue cases admitted to hospital. These values are lower than the case fatality rate for DSS, because the denominators include patients with less severe illness than DSS. The placebocontrolled, double-blind trial of steroid treatment for severe DSS by Tassniyom and colleagues2Tassniyom S Vasanawathana S Chirawatkul A Rojanasuphot F Failure of high dose methylprednisone in established dengue shock synndrome: a placebocontrolled, double-blind study.Pediatrics. 1993; 92: 111-115PubMed Google Scholar done in an academic setting in which there was management experience of DSS showed a case fatality rate of 12·7%. Among four other studies presented in that report, we referred only to the highest reported case-fatality rate, but our phrasing indicates that this is an extreme value (“can be as high as…”), and not the benchmark. The few reports available on the case fatality rate of DSS have small sample sizes, and may produce inaccurate estimates. We therefore hope that this discussion will encourage other researchers to report case-fatality rates in dengue patients with well characterised severity stages (such as hypotension or shock). Carerful attention to blood pressure in all patients should result in improved care, because the prognosis for DHF and DSS depends on prevention or early recognition and treatment of shock. Is there an inapparent dengue explosion?José Rigau-Perez and colleagues,1 inflation of global annual morbidity data and case fatality rates for dengue could have serious unintended consequences. In their introductory paragraphs, the investigators estimate 50–100 million dengue cases annually. A number of this magnitude was first suggested in 1988.2 It is becoming increasingly clear, however, that most dengue infections are inapparent. Although dengue fever is reported in only a few countries, comprehensive data for dengue haemorrhagic fever (DHF) and dengue shock syndrome (DSS) have been reported to regional offices of WHO for more than 30 years. Full-Text PDF