The new backpacks are broken in, the homework routine is set, and kids seem to be getting into the groove of a new school year. Everything is going predictably when you get a call from the school nurse: “You need to pick up your child.”

He went the whole summer without so much as a sniffle. Now, when he can't afford to miss school and you can't afford to miss work, he's sick. WebMD talked to medical experts about common ailments you can expect during the fall term, how to prevent them, and the latest information on immunizations.

When is Your Child Too Sick for School?

The Leading Ailments

Allergies. Fall is prime time for ragweed, molds, and other allergens. Kids with hay fever can still walk around and play sports, but the sneezing fits, itchy eyes, and fatigue can make them miserable and distracted. Your child's doctor can prescribe medication to manage the symptoms, and you can help your child avoid allergens. Wash bed linens weekly, avoid opening windows in your home and car, vacuum carpeting and rugs regularly, and keep kids from playing in piles of dead leaves.

Asthma. "Asthma is the leading chronic disease when it comes to kids missing school," says Michael Posner, MD, FAAP, spokesman for the American Academy of Pediatrics (AAP). Asthma is generally treated with preventive medication. The effectiveness of inhaled steroids or long-acting medications increases with use over time, reducing the likelihood that a respiratory infection or environmental changes will trigger asthma. "When kids show improvement, some parents think they're over the asthma, when in fact it's the medication keeping them well. Parents need to understand that kids must continue using the medication."

Develop an individualized asthma action plan with the school nurse, says Amy Garcia, RN, executive director of the National Association of School Nurses (NASN) in Silver Springs, Md. "Make the nurse aware of triggers, symptoms, medications, and what works with that child."

Marian Smithey, NASN nursing education director, says the plan will vary based on the severity of the child’s condition and the size of the school. "That's why the nurse working individually with the student is so important. Make sure your child has medications and devices to manage the asthma, knows what to do, and knows where to turn. All members of the school team having contact with your child should know what to do if the asthma is out of control.

Colds/sinusitis. Is it a cold that will simply run its course or a more complicated sinus infection that may need more aggressive treatment? That question perplexes pediatricians as well as parents. If your child has a history of sinusitis and comes down with a cold, you might think the doctor should prescribe an antibiotic. "Sinusitis looks like a cold," says Posner. "We define it as cold symptoms that haven't improved or are getting worse after 10 to 14 days. I can't diagnose it after a child has had a cold for just a few days. Physicians try very hard not to use antibiotics inappropriately because it increases bacterial resistance."

Gastroenteritis (stomach flu). When your child comes down with diarrhea and vomiting -- the characteristic signs of stomach flu -- take heed. Usually the cause is from a virus carried in the stool and is easily passed from one person to another. Here's where hand washing becomes a survival skill. Meanwhile, keep your sick child comforted and hydrated. If abdominal pain or fever is also present, make sure to seek medical attention to make sure it isn’t something more serious that would require more immediate and urgent attention.

Head lice. Myths persist about head lice. The truth is they are not a sign of poor hygiene, kids don't get them from pets, and they don't jump. Mainly they crawl from one head to another, feed on blood, and lay eggs, called nits, that hatch within one to two weeks.

Head lice thrive when kids go back to school, says Posner. "Kids are in such close contact, especially in preschool and kindergarten. They're pretty creepy, but they're not dangerous, and kids shouldn't be sent home in the middle of the school day. The child has probably had the lice for two weeks before the teacher even notices. Sending the child home won't significantly reduce the number of cases in the classroom."

"More schools are getting away from 'no nit' policies," says Marian Smithey, RN, education director for NASN. "If a child has live nits and the condition is being treated, they're better off in school."

Getting rid of head lice can be challenging. Smithey advises using an FDA-approved, over-the-counter treatment. "The pharmacist can help. Whatever you do, don't use dangerous home remedies like gasoline or a plastic bag over the child's head." Also, comb the lice and nits out of wet hair with a fine-toothed comb. Examine family members for lice, and keep your infested child from sharing pillows or combs with siblings or having head-to-head contact with others.

Pinkeye (conjunctivitis). Pinkeye appears as discomfort and redness in the eye, often along with a discharge and itchiness. Experts don't agree on what to do about it. "People get very excited about pinkeye," says Posner, who has a private pediatrics practice in West Springfield, Mass. "I've never been able to figure that out. Yes, it's highly contagious, but it doesn't cause a whole lot of trouble and by the time you notice it, the damage has already been done."

Smithey says it's not easy for the school nurse to tell whether the condition is due to allergies (red, itchy, watery eyes can also accompany allergies or hay fever) or infection, but if in doubt, the child should be sent home and seen by a physician. "If it's contagious, you don't want to spread it to other kids, and the child must be on medication for 24 hours before returning to school. If it's not contagious, the physician can write a note and they can come back to school."

See the doctor for an evaluation. A viral infection is often the cause of pinkeye, in which cases antibiotics (which fight bacteria) will not help. It will clear up on its own. If the doctor feels that the pinkeye is from a bacterial cause, then prescription antibacterial drops may be prescribed for treatment.

Preventive measures, such as good hand washing and not sharing personal items, such as towels or pillows, will help keep an infection from spreading at home.

Sore throat/strep throat. Most sore throats are caused by viruses and clear up on their own. Strep throat, which is very common among kids and teens, is a contagious bacterial disease generally accompanied by fever, swollen lymph nodes in the neck, and red, swollen tonsils. It often appears in the fall and peaks in January and February. Not all sore throats are from strep. A strep infection can be verified and diagnosed by special testing at the doctor’s office. Completion of an antibiotic course is extremely important in the treatment of strep to prevent complications such as rheumatic heart disease later.

Learn How to Keep Catchy Infections Contained

Preventing Contagious Illness

The best safeguard against kids catching something at school and sharing it with siblings is hand washing. "It's critical," says Posner. "There's probably no easy way to instill the habit. Parents and teachers just have to continually remind kids to wash their hands."

The CDC brochure "An Ounce of Prevention Keeps the Germs Away" outlines when and how to wash hands:

When to wash:

--Before, during, and after preparing food

--Before eating

--After using the bathroom

--After changing a diaper

--After handling animals, their toys, leashes, or waste

--After contact with blood or body fluids, such as vomit, nasal secretions, or saliva

--When your hands are dirty

--Before dressing a wound, giving medicine, or inserting contact lenses.

--More frequently if someone in your home is sick

--Whenever they look dirty

Visit WebMD's Health Center

How to wash:

--Wet hands and apply soap.

--Rub hands vigorously for 10 seconds. Imagine singing "Happy Birthday" twice.

--Rinse hands under running water.

--Dry hands with a paper towel or air dryer.

--If possible, use your paper towel to turn off faucet.

--If soap and water are not available, use an alcohol-based wipe or hand gel.

Besides proper hand washing, kids should learn not to share eating utensils or drinks. Garcia adds, "It's very important for kids to eat breakfast and get enough rest. Establish regular bedtimes. Teens, in particular, need more sleep than they get."

Six Serious Symptoms You Can't Ignore

The Latest on Immunizations

Thanks to universal vaccinations over several generations, dreaded diseases such as smallpox, polio, and diphtheria are rarely encountered in the Western world. But some diseases such as whooping cough and mumps have made a resurgence.

Perhaps the best news is there's now a booster vaccine for diphtheria, tetanus, and whooping cough (pertussis). "We've seen an increasing number of kids with whooping cough in middle school and high school in the past 15 years," says Posner. "It used to be that we couldn’t give booster shots after age 5, and by age 12, the effectiveness had waned."

Commenting on the cases of mumps on college campuses, Posner says, "Of all the vaccines, the mumps vaccine has the least take. We now give the vaccine twice -- at 12 months and again at age 4. It may be that college kids who got mumps didn't get the second dose." He adds that chickenpox (varicella) also is making a comeback. "Soon there will be a recommendation to repeat the chickenpox vaccination, as well."

A summer shortage of a vaccine against meningitis -- meningococcal conjugate vaccine (MCV4) -- caused the CDC and AAP to agree to defer recommended vaccination for kids aged 11 and 12. "Residential colleges are requiring students to be vaccinated, and the demand for vaccine was underestimated," says Posner. "Freshmen living in dorms are at the highest risk."

For children whose immunizations were up to date upon entering kindergarten, these are some vaccinations that may be due or administered if they were missed earlier according to the CDC’s "Recommended Childhood and Adolescent Immunization Schedule, U.S., 2006":

Hepatitis A (HepA) series. If not already vaccinated.

Hepatitis B series. If not already vaccinated

Measles, mumps, rubella. If not already completed.

Varicella (chickenpox). If not already vaccinated.

Influenza (flu). This changes every year.

Tetanus, diphtheria, pertussis (Tdap) booster.

Pneumococcal vaccine. If not already vaccinated.

Meningococcal vaccine. Unvaccinated students entering high school; college freshman living in dormitories.

WebMD Tool: Childhood Immunization Planner

By Leanna Skarnulis, reviewed by Louise Chang, MD

SOURCES: Amy Garcia, RN, executive director, and Marian Smithey, nursing education director, National Association of School Nurses, Silver Spring, Md. Michael Posner, MD, FAAP, spokesman, American Academy of Pediatrics, West Springfield, Mass. American Academy of Pediatrics web site. CDC: "Recommended Childhood and Adolescent Immunization Schedule, U.S., 2006"; "An Ounce of Prevention Keeps the Germs Away" brochure. WebMD Feature: "Keeping Catchy Infections Contained."