Severe respiratory illness of unexplained etiology during the 2009 influenza pandemic: Analysis of Clinical Features and Outcomes

Figures & data

Figure 1. Epidemic curve – number of H1N1-confirmed cases by episode date, Manitoba residents, April 2009 to January 2010.

Table 1. Number (%) of severe pH1N1 and SRI by wave, category and demographic characteristics, Manitoba residents.

	Wave 1			Wave 2			Total
	Severe pH1N1	Unexplained SRI	Explained SRI	Severe pH1N1	Unexplained SRI	Explained SRI	Severe pH1N1	Unexplained SRI	Explained SRI
Total	48	36	46	25	8	7	73	44	53
Age
<16	10 (20.8)	3 (8.3)	14 (30.4)	3 (12.0)	3 (37.5)	3 (42.9)	13 (17.8)	6 (13.6)	17 (32.1)
16–64	36 (75.0)	26 (72.2)	26 (56.5)	20 (80.0)	2 (25.0)	4 (57.1)	56 (76.7)	28 (63.6)	30 (56.6)
65+	2 (4.2)	7 (19.4)	6 (13.0)	2 (8.0)	3 (37.5)	0 (0.0)	4 (5.5)	10 (22.7)	6 (11.3)
Mean Age	38.3	47.9	36.9	39.0	36.4	24.9	38.5	45.8	35.3
Gender
Male	15 (31.3)	16 (44.4)	20 (43.5)	9 (36.0)	4 (50.0)	3 (42.9)	24 (32.9)	20 (45.5)	23 (43.4)
Female	33 (68.8)	20 (55.6)	26 (56.5)	16 (64.0)	4 (50.0)	4 (57.1)	49 (67.1)	24 (54.5)	30 (56.6)
Ethnicity
Caucasian	12 (25.0)	10 (27.8)	14 (30.4)	13 (52.0)	2 (25.0)	4 (57.1)	25 (34.2)	12 (27.3)	18 (34.0)
Métis	1 (2.1)	2 (5.6)	2 (4.3)	0 (0.0)	2 (25.0)	0 (0.0)	1 (1.4)	4 (9.1)	2 (3.8)
First Nations	25 (52.1)	15 (41.7)	17 (37.0)	3 (12.0)	1 (12.5)	3 (42.9)	28 (38.4)	16 (36.4)	20 (37.7)
Other	3 (6.3)	4 (11.1)	3 (6.5)	1 (4.0)	1 (12.5)	0 (0.0)	4 (5.5)	5 (11.4)	3 (5.7)
Unknown	7 (14.6)	5 (13.9)	10 (21.7)	8 (32.0)	2 (25.0)	0 (0.0)	15 (20.5)	7 (15.9)	10 (18.9)
Region
Winnipeg Health Region	20 (41.7)	17 (47.2)	28 (60.9)	11 (44.0)	3 (37.5)	4 (57.1)	31 (42.5)	20 (45.5)	32 (60.4)
Northern RHAs^*	18 (37.5)	9 (25.0)	11 (23.9)	2 (8.0)	0 (0.0)	2 (28.6)	20 (27.4)	9 (20.5)	13 (24.5)
Rest of province	10 (20.8)	10 (27.8)	7 (15.2)	12 (48.0)	5 (62.5)	1 (14.3)	22 (30.1)	15 (34.1)	8 (15.1)

* Northern RHAs include North Eastman, Norman, Burntwood and Churchill RHAs

Table 2. Number (%) of severe pH1N1 and SRI by wave, category and clinical features, Manitoba residents.

	Wave 1			Wave 2			Total
	Severe pH1N1	Unexplained SRI	Explained SRI	Severe pH1N1	Unexplained SRI	Explained SRI	Severe pH1N1	Unexplained SRI	Explained SRI
Presenting Symptoms and Signs
Total	48	36	46	25	8	7	73	44	53
Meets ILI case definition	47 (97.9)	13 (36.1)	6 (13.0)	25 (100.0)	3 (37.5)	1 (14.3)	72 (98.6)	16 (36.4)	7 (13.2)
Cough	36 (75.0)	27 (75.0)	29 (63.0)	19 (76.0)	8 (100.0)	5 (71.4)	55 (75.3)	35 (79.5)	34 (64.2)
Fever	40 (83.3)	30 (83.3)	29 (63.0)	22 (88.0)	6 (75.0)	7 (100.0)	62 (84.9)	36 (81.8)	36 (67.9)
Myalgia	12 (25.0)	10 (27.8)	5 (10.9)	8 (32.0)	3 (37.5)	0 (0.0)	20 (27.4)	13 (29.5)	5 (9.4)
Shortness of breath	36 (75.0)	33 (91.7)	28 (60.9)	22 (88.0)	6 (75.0)	3 (42.9)	58 (79.5)	39 (88.6)	31 (58.5)
Mortality
Total	48	36	46	25	8	7	73	44	53
Death	8 (16.7)	5 (13.9)	7 (15.2)	2 (8.0)	1 (12.5)	2 (28.6)	10 (13.7)	6 (13.6)	9 (17.0)
Death linked to respiratory illness of all deaths	6 (75.0)	4 (80.0)	2 (28.6)	1 (50.0)	1 (100.0)	2 (100.0)	7 (70.0)	5 (83.3)	4 (44.4)
Death linked to respiratory illness of all cases	6 (12.5)	4 (11.1)	2 (4.3)	1 (4.0)	1 (12.5)	2 (28.6)	7 (9.6)	5 (11.4)	4 (7.5)
Protective Factors
Total	48	36	46	25	8	7	73	44	53
Received trivalent influenza vaccine in 08/09	10 (20.8)	10 (27.8)	12 (26.1)	5 (20.0)	0 (0.0)	3 (42.9)	15 (20.5)	10 (22.7)	15 (28.3)
Received trivalent influenza vaccine in 09/10	not available			4 (16.0)	0 (0.0)	0 (0.0)	4 (5.5)	0 (0.0)	0 (0.0)
Received the Pandemic H1N1 influenza vaccine	not available			3 (12.0)	0 (0.0)	1 (14.3)	3 (4.1)	0 (0.0)	1 (1.9)
Treated with antivirals	40 (8.3.)	30 (83.3)	25 (54.3)	19 (76.0)	7 (87.5)	5 (71.4)	59 (80.8)	37 (84.1)	30 (56.6)
Antivirals started within 2 d of onset	6 (12.5)	1 (2.8)	0 (0.0)	6 (24.0)	0 (0.0)	0 (0.0)	12 (16.4)	1 (2.3)	0 (0.0)

Table 3. Provincial case definitions.

Influenza-like illness (ILI)	Fever >38 C AND cough AND one or more of sore throat, arthralgias, myalgias or prostration.^*
Severe ILI	Acute onset of respiration illness with fever and cough and one or more of the following: sore throat, arthralgias, myalgias or prostration which could be due to influenza virus, and include complications such as encephalitis or other severe and life-threatening complications.^**
Severe respiratory illness (SRI)
First wave	ILI symptoms with worsening cough, dyspnea, atypical pneumonia on CXR or Acute Respiratory Distress Syndrome. Admission to hospital is required to support these patients.^***
Second wave	All of the following:
	• Admission to hospital
	• Fever >38 C
	• New onset of (or exacerbation of chronic) cough or breathing difficulty
	• Admission to ICU/other area of the hospital where critically ill patients are cared for OR mechanical ventilation with evidence of severe illness progression (either radiographic evidence of infiltrates consistent with pneumonia or a diagnosis of Acute Respiratory Distress Syndrome/severe ILI)
	• No alternate diagnosis within the first 72 hours of hospitalization

* Fever may be muted in patients under age 5, those undergoing cancer and blood disorder treatments, or with receipt of antipyretics, corticosteroids or immunosuppressive drugs. In children under age 5, gastrointestinal symptoms may also be present and cough may not be prominent; children may also present with respiratory compromise, altered mental status and neurologic findings, or evidence of sepsis. Neonates may present with apnea, cyanosis, poor feeding, lethargy and sepsis.

** (In children under age 5, cough may not be prominent and gastrointestinal symptoms may also be present. In patients under 5 or over 65, fever may not be prominent.)

*** This definition was operationalized in different ways but usually requiring fever and cough or shortness of breath AND admission to ICU or ventilation.(1)