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Now that routine testing for the H1N1 virus has become logistically impossible for most patients, doctors must base their diagnosis largely on the clinical presentation of the patient, the use of RIDTs (Rapid Influenza Diagnostic Tests), and the current level of flu activity in the community.
From PloS Currents, we get a study conducted at the Infectious Diseases and Tropical Medicine department of Marseille university hospital that looked at the RIDT (Rapid Influenza Diagnostic Tests) and clinical signs and symptoms of patients that tested positive via RT-PRC testing for the H1N1 virus.
Of the 307 patients evaluated with flu-like symptoms, 31 tested positive for H1N1. Or an incidence level of about 10%. Further evidence that not all ILI’s over the summer were H1N1 (see ILI’s Aren’t Always The Flu).
While many patients without H1N1 presented with a cough, of those that tested positive for the virus, 100% had a cough. Asthenia (weakness, loss of strength) was present in 97% of cases, and fever in 87%.
Myalgia was significantly higher in non-flu ILI’s (90%) than among the confirmed H1N1 cases (64%)
The authors theorize:
. . . a patient who present with a flu-like illness and cough should systematically be tested by RIDT because the presence of cough is associated with a sensitivity at 100%. This clinical sign alone will not be predictive of the disease as the PPV is low and will stay low even during the epidemic (Figure 3A).
However the association of cough, diarrhoea and the lack of myalgia, although not useful in the early phase, may be useful in the acme of the epidemic as the PPV reaches up to 90% when the prevalence exceeds 20%.
Although based on a relatively small cohort of positive H1N1 patients (n=31), this study gives us an interesting overview of their clinical signs and symptoms.
A few highlights below, but follow the link to read the study in its entirety.
Improving the diagnostic efficiency of H1N1 2009 pandemic flu: analysis of predictive clinical signs through a prospective cohort.
BROUQUI, Philippe; VU HAI, Vinh; NOUGAIREDE, Antoine; LAGIER, Jean-Christophe; BOTELHO, Elisabeth; NINOVE, Laetitia; ZANDOTTI, Christine; CHARREL, Remi N.; DE LAMBALLERIE, Xavier; RAOULT, Didier. Improving the diagnostic efficiency of H1N1 2009 pandemic flu: analysis of predictive clinical signs through a prospective cohort
[Internet]. Version 24. PLoS Currents: Influenza. 2009 Oct 21. Available from: http://knol.google.com/k/philippe-brouqui/improving-the-diagnostic-efficiency-of/qccicvnl16mc/1.
In late June 2009, we set up a dedicated flu-like illness outpatient consultation in the Infectious Diseases and Tropical Medicine department of Marseille university hospital to detect the new A/H1N1 pandemic influenza and to contain efficiently the A/H1N1 infected patients.
For 3 months, we compiled data corresponding to a total of 307 patients who presented with a flu-like syndrome. 31 of them were positive for H1N1 pandemic flu through real-time RT-PCR (rRT-PCR); among them, 19 were positive for a rapid influenza detection test (RIDT). We report here the significant clinical characteristics of A/H1N1 pandemic flu patients compared with other flu-like illnesses, which were used to improve the predictive value of the diagnosis in the current epidemiological situation.
We found that regardless of the prevalence of A/H1N1 positive cases in the suspected patients, the absence of cough rejects the diagnosis of A/H1N1 infection in 100% of cases. Among patients referred for flu-like illness, those with cough should be tested for A/H1N1 by RIDT.
Interestingly, myalgia was significantly associated with “non-Flu” patients (20/46%) with a Relative Risk of 0.42. All other clinical signs including fever, asthenia, headaches, and vomiting were not significantly associated with “Flu patient” (Table 1).
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