H1N1 Flu: Shift to Easier Testing/Tamiflu?

H1N1 has established foothold, Health Minister says

New Straits Times online: 2009/08/07

KUALA LUMPUR: Saying influenza A (H1N1) had “established a foothold” in Malaysia, Health Minister Datuk Seri Liow Tiong Lai yesterday announced three new strategies to counter the pandemic.

The new measures are aimed at making H1N1 testing and treatment more widely available and accessible to the public, and will take immediate effect.

The three new strategies are:

• all clinics and hospitals, both private and public, are encouraged to use rapid influenza screening tests for those with flu-like symptoms who request to be tested. Such tests should be done as close as possible to the onset of symptoms. All cases testing positive for H1N1 can be treated immediately with the antiviral oseltamivir.
• 
  
• all clinics and hospitals, both private and public, can now treat patients suspected of having contracted H1N1 with oseltamivir. This is particularly essential for those who test positive on the rapid test and those with risk factors and co-morbidities. However, those with more severe illness, with associated risk factors and co-morbidities, should be referred to hospitals for treatments; and,
• 
  
• the ministry will make all efforts to ensure the supply of antiviral in the market would not be disrupted.
  

A statement issued by the ministry yesterday, however, pointed out that the rapid tests are only 70-75 per cent accurate and advised patients with flu-like symptoms but tested negative for influenza A to also observe all precautions and seek further treatment if their condition worsened. (Actually it's considerably lower than that, see below...)

The statement said the Ministry will also stop daily reporting on the number of tested and confirmed cases in Malaysia, in line with the World Health Organisation’s stand in stopping such reports.

This is because the WHO feels that such reports no longer give an accurate view of the actual situation on the ground.

“However, we will continue to report the number of cases admitted in our hospitals for inpatient treatment and deaths,” said the statement, adding that the ministry would continue to monitor and report on cluster outbreaks to make sure preventive measures can be put in place quickly.

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But consider the following study announced by the CDC, USA in its Morbidity & Mortality Weekly Report, MMWR (August 7, 2009 / 58(30);826-829)

Evaluation of Rapid Influenza Diagnostic Tests for Detection of Novel Influenza A (H1N1) Virus --- United States, 2009

TABLE 1. Comparison of the number of positive influenza A test results from three RIDTs* with the number of positive results from rRT-PCR† assay, by influenza A type and cycle threshold (Ct) interval --- United States, 2009
RIDT	Influenza A virus type	No. of specimens positive by RIDT/ No. positive by rRT-PCR				Total no. of specimens positive by RIDT/ Total no. positive by rRT-PCR	(%)
		Ct interval§
		(<20)	(20 to <25)	(25--30)	(>30)
BinaxNOW Influenza A&B	Novel H1N1	8/9	7/17	2/13	1/6	18/45	(40)
	Seasonal H1N1	---¶	2/3	1/2	---	3/5	(60)
	Seasonal H3N2	---	10/10	2/4	0/1	12/15	(80)
Directigen EZ Flu A+B	Novel H1N1	8/9	10/16	2/12	1/6	21/43**	(49)
	Seasonal H1N1	---	2/2	1/2	---	3/4**	(75)
	Seasonal H3N2	---	8/8	2/3	0/1	10/12**	(83)
QuickVue A+B	Novel H1N1	9/9	13/17	6/13	3/6	31/45	(69)
	Seasonal H1N1	---	2/3	2/2	---	4/5	(80)
	Seasonal H3N2	---	10/10	2/4	0/1	12/15	(80)
* Rapid influenza A diagnostic tests. † Real-time reverse transcription--polymerase chain reaction. § A Ct value of 37 or lower is considered a positive rRT-PCR result. ¶ No data available. ** For this RIDT, insufficient material was available to test two specimens that were rRT-PCR positive for novel H1N1, one for seasonal H1N1, and three for seasonal H3N2 ------------------------------------------------------------------------------------------------------------------

TABLE 2. Limits of detection of Madin-Darby canine kidney (MDCK)--grown influenza A/California/4/2009 (H1N1) for three rapid influenza diagnostic tests (RIDTs), by selected measurement values --- United States, 2009
	Values
RIDT	Lowest dilution with positive result	TCID50/ mL*	Ct†
BinaxNOW Influenza A&B	10-2	10 5.5	22.15
Directigen EZ Flu A+B	10-3	10 4.5	26.05
QuickVue A+B	10-3	10 4.5	26.05
* TCID50 = 50% tissue culture infectious dose. † Ct (cycle threshold) values reported as an average of three reactions each of duplicate dilution series.

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Summary from Physician's First Watch:

H1N1 Update: Rapid Diagnostic Tests Have Low Overall Sensitivity for Novel Influenza A Virus

Preliminary data from the CDC suggest that rapid influenza diagnostic tests have a low overall sensitivity for novel influenza A (H1N1), MMWR reports.

Sixty-five respiratory specimens that tested positive for novel influenza A (H1N1) or seasonal influenza A (H1N1 or H3N2) by reverse-transcription polymerase chain reaction were tested again using three rapid tests.

Among the findings:

• Overall sensitivity for novel influenza A ranged from 40% to 69%.
• For nine specimens with high viral titers of novel influenza A, sensitivity ranged from 89% to 100%.
• The tests were generally more sensitive for seasonal flu (range, 60% to 83%) than for novel influenza A.

An editorial note concludes that, for now, all results from rapid tests in suspected H1N1 cases "should be interpreted in the context of circulating influenza virus strains in the patient's community, level of clinical suspicion, severity of illness, and risk for complications."