Maricopa County
Department of Public Health

2010 Outbreak Summary Report

Office of Epidemiology
August 2011

Table of Contents
Introduction ............................................................................................................................................. 3
Investigation Methodology ................................................................................................................... 4
Investigation Analysis ........................................................................................................................... 5
Specimen Collection........................................................................................................................... 112
Specimen Demographics ..................................................................................................................... 15
Conclusions and Recommendations ................................................................................................. 17

Introduction
The purpose of this report is to provide an overview of the disease outbreaks reported
throughout 2010 in Maricopa County, Arizona and the subsequent investigations led by the
Maricopa County Department of Public Health (MCDPH). In Arizona, health care providers
(HCPs), health care institutions (HCIs), correctional facilities (CFs), childcare establishments
(CCEs), administrators of schools and shelters are all required to report outbreaks of infectious
diseases to the MCDPH under Arizona Administrative Code A.A.C. R9‐6‐203 and ARS Title
36. Outbreaks involving certain illnesses require that facilities notify the health department
within 24 hours after the existence of the illness is known. In addition, operators of hotels,
motels, and resorts are required to notify the MCDPH regarding any reports of contagious,
infectious, or epidemic disease within 24 hours “after the existence of the disease is known” i
under Arizona Revised Statutes Title 36, Chapter 6, Article 2. Table 1 below displays the
diseases requiring notification within 24 hours of receiving a report of a case, suspected case,
or detecting an outbreak.

Table 1. Diseases requiring outbreak notification within 24 hours in Arizona
Reporting by HCPs, HCIs,
Reporting by Schools, CCEs, and
Disease/Condition
and CFs
Shelters
Amebiasis
X*
Campylobacteriosis
X*
Conjunctivitis: acute
X
X*
Cryptosporidiosis
X*
X*
Diarrhea, Nausea, or Vomiting
X
X
Enterohemorrhagic E. coli
X*
Giardiasis
X*
Hepatitis A
X*
X*
Measles
X*
Mumps
X*
Pertussis
X*
Rubella
X*
Salmonellosis
X*
X*
Scabies
X
X
Shigellosis
X*
X*
Streptococcal Group A Infection
X
Taeniasis
X*
Vibrio Infection
X*
Yersiniosis
X*
*Within 24 hours after detecting a case or suspecting a case (in a food handler, CCE worker or HCI worker)

3

Investigation Methodology
Outbreaks occur when two or more unrelated cases (individuals showing signs and/or
symptoms of the illness associated with the outbreak) are linked to a common exposure (e.g.
two parties who are unknown to each other becoming ill after eating at the same restaurant or
two friends who have not had contact with each other experiencing vomiting after dining at a
restaurant together). MCDPH investigates outbreaks in order to identify the source of disease,
quickly isolate and stop the spread of disease, and prevent future outbreaks. MCDPH also
investigates single case reports of communicable diseases, which often leads to the
identification of additional cases that may turn out to be part of an outbreak. After the
identification of an outbreak, MCDPH provides educational materials to help stop the
transmission and to provide information on preventing future disease outbreaks.
MCDPH investigates outbreaks in conjunction with other agencies in Maricopa County such
as the Maricopa County Department of Environmental Services (ES) which also conducts
investigations and inspections of facilities involved in the reports of outbreaks. Additionally,
many outbreak investigations require the assistance of the Arizona Department of Health
Services (ADHS) which provides epidemiological support and laboratory services for the
specimens collected during an outbreak investigation. When indicated, and if possible,
MCDPH and/or ES will collect biological and environmental specimens as part of these
investigations to obtain precise laboratory information and facilitate intervention. All outbreak
reports are submitted to ADHS, and then forwarded to the Centers for Disease Control and
Prevention (CDC).
Due to limited resources, MCDPH cannot investigate all outbreaks that are reported. MCDPH
epidemiologists conduct risk assessments to weigh several factors to determine if an outbreak
will be investigated. The following factors are examined for each outbreak to determine
whether an investigation should occur:
•
•
•
•
•
•
•
•

Number of people ill
Severity of illness
Illness resulting in death, disability, or hospitalization
Timeliness of the report
Availability of specimens
The level of vulnerability of affected individuals
Type of facility
The degree to which the outbreak is under control

The timely collection of stool specimens from ill individuals is essential in identifying the
etiology of gastrointestinal outbreaks. Specimens need to be collected while the pathogen
(infectious agent) can be isolated in the stool sample. Without a stool specimen, the identity of
the pathogen that caused the illness will probably not be identified.

4

Investigation Analysis
In 2010, there were 144 outbreaks investigated in Maricopa County or an average of 12 outbreaks per
month, with the number of outbreaks peaking in April and May and again in November and December
(see Figure 1); this is a decrease from the monthly average of 13.3 in 2009. In 2008, there were

139 outbreaks, an average of 11.6 per month ranging from 4 to 25 per month. As shown in
Figure 1, reports of outbreaks from 2008 to 2009 followed a bimodal distribution with peaks in
the spring and fall months, while 2010 was more typically distributed with an increase in
outbreaks in April and May. In 2009, MCDPH encouragement and media reports on the novel
H1N1 influenza pandemic caused schools to increase reporting on influenza‐like illnesses
(ILIs), which most likely contributed to the increase in outbreak reporting during the spring
and fall of 2009. In 2010, gastrointestinal illnesses predominated as 19 of the 27 reports of
outbreak in May were for gastrointestinal illness (see Figure 2.) This pattern is more typical of
outbreak reporting patterns prior to 2009.

Figure 1. Number of Outbreaks Report by Month
2008 ‐ 2010

Number of Outbreaks

2008 (n=139)

2009 (n=160)

30
25
20
15
10
5
0

Month

5

2010 (n=144)

In 2010, the median number of persons ill per outbreak was 23, which was less than it was in
2009 (median = 28.5) and 2008 (median = 24). In 2010, 116 of the 144 outbreaks (81%) affected
20 or fewer persons (see Figure 3).

Figure 3. Number of Persons Ill Per Outbreak
2008 ‐ 2010
2008 (n=139)

2009 (n=160)

2010 (n=144)

Number of Outbreaks

60
50
40
30
20
10
0
<5

5‐10

11‐20

21‐50

51‐100

Number of Persons Ill per Outbreak

6

101+

Table 2 shows the number of outbreaks by etiology for the past three years. Of the total 144
outbreaks investigated in 2010, there were 108 outbreaks in which the etiology was known
(75% of the total), and 36 (25% of the total) of unknown etiology. Comparatively, in 2009, 13%
of the outbreaks were of unknown etiology and in 2008, 23% were unknown. Influenza‐like
illness outbreaks are counted as known etiology since ILI surveillance is routinely conducted
as a proxy for influenza activity. The classification of ILI outbreaks as “known etiology”
increased the percentage of outbreaks with known etiology in 2009.
Table 2. Number of Outbreaks by Type and Etiology
2008
2009
Known/Unknown Etiology
33 (23%)
22 (13%)
Unknown etiology
Unknown (Gastrointestinal Illness)
33 (23%)
22 (13%)
Unknown (Rash)
0 (0%)
0 (0%)
106 (77%) 138 (87%)
Known etiology
Outbreak by Known Etiology/Symptoms
Gastrointestinal
Cryptosporidiosis
E. coli
Giardiasis
Norovirus
Rotavirus
Salmonella
Shigella
Unknown (Gastrointestinal Illness)
Infection
Conjunctivitis
Hand, Foot, and Mouth Disease
Strep Group A (Strep Throat)
Rash
Fifths Disease (Human Parvovirus B19)
Head Lice
Methicillin‐resistant Staphylococcus Skin Infection
Scabies
Varicella
Unknown (Rash)
Respiratory
ILI (Influenza‐like Illness)
Influenza
Respiratory Syncytial Virus (RSV)
Other
Aseptic Meningitis
Mercury contamination
Grand Total

7

82(59%)
5 (4%)
0 (0%)
0 (0%)
33 (23%)
1 (1%)
2 (1%)
8 (6%)
33 (23%)
6 (4%)
3 (2%)
0 (0%)
3 (2%)
44 (32%)
1 (1%)
6 (4%)
2 (1%)
11 (8%)
24 (17%)
0 (0%)
6 (4%)
2 (1%)
2 (1%)
2 (1%)
1 (1%)
1(1%)
0 (0%)
139
(100%)

73 (46%)
0 (0%)
1 (1%)
1 (1%)
27 (17%)
0 (0%)
12 (8%)
10 (6%)
22 (14%)
8 (5%)
2 (1%)
1 (1%)
5 (3%)
22 (14%)
1 (1%)
0 (0%)
1 (1%)
7 (4%)
13 (8%)
0 (0%)
56 (35%)
50 (31%)
2 (1%)
4 (3%)
1 (1%)
0 (0%)
1 (1%)
160
(100%)

2010
36 (25%)
35 (24%)
1 (1%)
108 (75%)

86 (60%)
0 (0%)
2 (1%)
0 (0%)
44 (31%)
0 (0%)
5 (4%)
0 (0%)
35 (24%)
13 (9%)
5 (4%)
2 (1%)
6 (4%)
43 (30%)
0 (0%)
4 (3%)
0 (0%)
16 (11%)
22 15%)
1 (1%)
2 (1%)
1 (1%)
1 (1%)
0 (0%)
0 (0%)
0 (0%)
0 (0%)
144
(100%)

While the specific etiology of an outbreak is not always determined, most outbreaks can be
broadly classified based on the symptoms exhibited by cases. Table 2 shows that from 2008
through 2010, the most frequent outbreak type investigated by the MCDPH was
gastrointestinal, although there were nearly as many respiratory outbreaks reported in 2009.
The “other” category for outbreak type includes an outbreak of meningitis in 2008 and a
mercury contamination that occurred in 2009. The pathogen that was most often isolated from
specimens gathered from outbreaks was norovirus.
As seen in Figure 4, food establishments, senior living facilities, and schools were the most
common type of facility for which outbreaks were reported. The daycare/shelter category
included childcare facilities and shelters, the food establishment category included restaurants
and caterers, the hospital/clinic category included psychiatric in‐patient facilities and clinics,
the prison/jail category included juvenile detention centers as well as adult prison facilities,
and the schools category included preschools, public and private schools. The senior living
facility category includes long‐term care facilities, assisted living facilities and acute care
facilities and the “other” category includes countywide outbreaks (for which no specific
facilities were identified), sports teams, military bases and public pools.

Figure 4. Number of Outbreaks by Facility

2008 ‐ 2010
Number of Outbreaks

80
60
40
20
0

Daycare
/ Shelter

Food Est.

Hospital
/ Clinic

Prison /
Jail

Resort /
Hotel

School

Work
site

32

Senior
Living
Facility
26

2008 (n=139)

25

34

11

4

1

2009 (n=160)

25

29

2

3

2

2010 (n=144)

16

39

4

3

4

Other

1

5

67

20

1

11

35

37

1

5

Facility

The number of outbreaks by type of outbreak and facility are shown in Figure 5. Rash illness
outbreaks were the most common type of outbreak in schools and prisons/jails, with varicella
(“chickenpox”) being the most common illness. In contrast, outbreaks reported in daycares/
shelters, hospitals/clinics, resorts/hotels, senior living facilities, and food establishments were
more likely to be gastrointestinal illness outbreaks, with norovirus again being the most

8

common gastrointestinal illness (see Figure 6). There were also outbreaks of infections
reported in schools, daycares/shelters, hospitals/clinics, and senior living facilities (see Figure 9
for specific types of infections). The most common type of infection outbreak was strep throat,
while there were only two reported outbreaks of respiratory illness (influenza and ILI) in a
school and senior living facility, respectively. This is a decrease in respiratory outbreaks from
2009 (56 outbreaks), which were attributed to the novel H1N1 influenza pandemic mentioned
earlier in the report.
It is important to note that while schools and senior living facilities are required by law to
report outbreaks to Maricopa County, reports related to food establishments are gathered
using a different method. As described earlier, individuals who believe they became ill from
eating at a restaurant call the Department of Environmental Services. Sometimes it turns out
that the complainant became ill from person‐to‐person spread or from food eaten elsewhere.
Thus, some of the outbreaks here are only equivocally attributed to the food establishment.

Figure 5. Number of Outbreaks by Type and Facility

2010

Number of Outbreaks

Gastrointestinal

Infection

Rash

Respiratory

40
35
30
25
20
15
10
5
0

Facility

Figure 6 shows the number of gastrointestinal outbreaks by etiology and type of facility. The
percentage of gastrointestinal outbreaks with an unknown etiology was most likely due to a
lack of specimens for lab testing, or untimely reporting of outbreaks.

9

Figure 6. Number of Outbreaks by Etiology & Facility: GI (n=86)

2010
Number of Outbreaks

E. coli

Norovirus

Salmonella

Unknown (Gastrointestinal Illness)

20
15
10
5
0

Type of Facility

Figure 7 shows the number of rash outbreaks by etiology and facility type for 2010. Varicella
and scabies were the most common etiologies with schools and senior living facilities having
the highest number of outbreaks. All of the rash outbreaks at senior living facilities were
scabies, while schools had reports of varicella and head lice.

Figure 7. Number of Outbreaks by Etiology & Facility: Rash (n=43)

2010

Number of Outbreaks

Head Lice

Scabies

Unknown (Rash)

20
15
10
5
0

Type of Facility

10

Varicella

In Figures 8 and 9 respiratory and infection outbreaks by facility are shown for 2010. Again,
schools were the most common locations for these types of outbreaks with most of the
etiologies being common childhood illnesses.

Number of Outbreaks

Figure 8. Number of Outbreaks by Etiology &
Facility: Respiratory (n=2)
2010
ILI

Influenza

1

0.5
0
School

Senior Living Facility
Type of Facility

Figure 9. Number of Outbreaks by Etiology & Facility: Infection (n=13)

2010
Conjunctivitis

Hand, Foot, and Mouth Disease

Strep Group A (Strep Throat)

Number of Outbreaks

3
2.5
2
1.5
1
0.5
0
Daycare/Shelter

Hospital/Clinic
Type of Facility

11

School

Senior Living Facility

Specimen Collection
MCDPH was able to collect one or more specimens for 61 of the 86 gastrointestinal outbreaks
that were reported in 2010. This is at least one specimen for 71% of the GI outbreaks. A total of
104 stool specimens were collected for the 61 outbreaks; this is an average of 1.7 specimens per
outbreak.
Specimens were not collected for 25 of the 86 GI outbreaks. The most likely reasons specimens
were not obtained were too much time elapsing between an event and the report of illness,
unwillingness by some cases to provide a specimen for testing, and/or the inability by MCDPH
to contact some of the cases involved in an outbreak.
There were 123 specimen collection kits provided to cases by MCDPH, with a range of 1‐5 kits
provided per outbreak. Of the 123 kits delivered, 104 or 84% of the recipients returned stool
specimens for analysis. These specimens were submitted for testing to the Arizona State
Laboratory (ASL). Figure 10 shows the distribution of specimens submitted and tested at ASL
in 2010 by month.

Of the 104 stool specimens submitted to the Arizona State Laboratory for testing, 101 (97%)
were tested for norovirus alone or norovirus and other pathogens, and three (3%) were tested
for influenza. Among the 101 specimens tested for norovirus, 12 (or 12%) were also tested for
bacterial pathogens (E. coli, Campylobacter, Shigella, and Salmonella), and one specimen was
tested for rotavirus. In total, 78 specimens tested positive for norovirus (see distribution in
Figure 11). In addition to these laboratory tests performed at the Arizona State Laboratory
(ASL), there was one test performed at a laboratory other than the ASL. This sample did not
result in the positive identification of a pathogen.

12

Figure 11. Total Number of Specimens that Tested
Positive for Norovirus by Month (n=44)
2010
Number of Specimens

Norovirus ‐ GI

Norovirus ‐ GII

Norovirus ‐ GII & GI

Norovirus ‐ Unknown

8
6
4
2
0

Month

Outbreaks of norovirus were most common in senior living facilities and food establishments,
as shown in Figure 12. Again, please note that the outbreaks attributed to food establishments
may include some outbreaks for which the source was not actually a food establishment but
rather person‐to‐person spread or food from another source. These are listed in this report as
associated with a food establishment because they were identified by individuals who, at least
initially, believed they became sick from a food establishment.

Figure 12. Number of Norovirus Outbreaks by
Facility (n=44)
2010
Senior Living
Facility
36%
School
11%

13

Daycare/Shelter
9%
Food
Establishment
37%
Resort/Hotel
7%

The numbers of reported norovirus outbreaks by number of persons ill are shown in Figure 13.
The majority of outbreaks (69%) affected more than 10 individuals, with eight occurring in
groups of greater than 50 individuals.

Figure 13. Number of Norovirus Outbreaks by
Number of Persons Ill (n=44)
2010
Number of Outbreaks

12
10
8
6
4
2
0
Total

<5
7

5‐10
11

11‐20
10

21‐50
8

Number of Persons Ill

14

51‐100
7

101+
1

Specimen Demographics
As shown in Figure 14, of the specimens submitted, most (43%) were from cases between the
ages of 20 and 74 followed by cases over the age of 75 (38%). This correlates with Figure 12
above, which shows that 36% of the specimens submitted were from senior living facilities.

Figure 14. Percentage of Specimens Submitted by Age
Range of Donors (n=104)

2010
38%

19%

Age Range of 1‐19 Years Old

43%

15

Age Range of 20‐74 Years
Old
Age Range of > 75 Years Old

As shown in Figure 15, females (61%) were more likely to submit a specimen than males (39%);
even though individuals involved in outbreaks were evenly split between males and females
(43% Female versus 42% Male) as seen in Figure 15.

Figure 15. Percentage of Specimens Submitted by
Sex (n=104)
2010
Female

Male

39%

61%

16

Conclusions and Recommendations
•

Foodborne and waterborne illnesses are common in Maricopa County and the data
shown here represent just a fraction of the outbreaks that actually occur. For example,
the Centers for Disease Control (CDC) and Prevention estimate that in the United
States, more than 21 million cases of acute gastroenteritis each year are due to norovirus
infection, and more than 50% of all foodborne disease outbreaks can be attributed to
noroviruses; however, only 600 outbreaks were confirmed by the CDC between 1994
and 2006. ii Norovirus is not a nationally notifiable condition because testing for the
disease is not generally available in hospitals and doctor’s offices; norovirus is usually
diagnosed only when an outbreak (the occurrence of two or more similar illnesses
resulting from ingestion of a common food”) occurs. iii

•

Norovirus was the pathogen that was most frequently positively identified as
contributing to illness outbreaks. Given the prevalence of norovirus in outbreaks and
presumably in the community, more effort should be expended on educating the public
on preventing the spread of gastrointestinal illness and communicable illnesses in
general (e.g. proper handwashing practices, how and when to use antibacterial gel,
etc.).

•

In 2010, outbreaks commonly occurred where people were congregated for long periods
each day – long‐term care facilities, schools, etc. Appropriate control measures should
be encouraged in these settings, which includes, but is not limited to, proper hand
washing, routine cleanliness in areas at risk of contamination (e.g. kitchens, bathrooms,
etc.), removal or cleanliness of shared items (especially in a classroom setting), use of
chlorine based cleaners, isolating ill persons to limit transmission, and ensuring that all
food handlers with signs of illness (e.g. diarrhea or vomiting) are excluded from work.

•

The percent of outbreaks with an unknown etiology started to decline in 2007 due to an
increase in specimen submissions; however, outbreaks of unknown etiology increased
slightly between 2009 (13%) and 2010 (25%). MCDPH intends to continue its attempts at
collecting specimens for as many outbreaks as possible in order to resume the
downward trend. As bacterial pathogens are very rarely isolated during testing of stool
specimens, bacterial testing is limited only to instances where evidence for a bacterial
pathogen exists (e.g., when a case has bloody stools or the incubation period is
consistent with a bacterial pathogen).

•

Since 2007, there has been a steady rise in the number of outbreaks each year; although,
the number of outbreaks in 2010 (144) was less than the number of outbreaks reported

17

in 2009 (160) due to the influenza pandemic in 2009. Additional resources are needed in
order for MCDPH to investigate each outbreak adequately and in order to handle
unexpected outbreaks associated with emerging and/or pandemic diseases such as the
2009 Influenza Pandemic. The number of uninvestigated outbreaks will likely increase
annually if appropriately trained staff members are not added.

i

Arizona State Legislature: http://www.azsos.gov/public_services/Title_09/9-06.htm
Centers for Disease Control: http://www.cdc.gov/ncidod/dvrd/revb/gastro/norovirus-factsheet.htm
iii
Centers for Disease Control: http://www.cdc.gov/ncidod/dvrd/revb/gastro/norovirus-surv-disease-burden.htm
ii

18